Solid Electrolyte, Method For Producing Solid Electrolyte, And Composite Body

ABSTRACT

A solid electrolyte according to the present disclosure is represented by the following compositional formula (1).Li7-2x-zLa3(Zr2-x-zWxMz)O12  (1)In the formula (1), x and z satisfy 0.10≤x≤0.60 and 0.00&lt;z≤0.25, and M is at least one type of element selected from the group consisting of Nb, Ta, and Sb.

The present application is based on, and claims priority from JPApplication Serial Number 2020-040697, filed on Mar. 10, 2020, thedisclosure of which is hereby incorporated by reference herein in itsentirety.

BACKGROUND 1. Technical Field

The present disclosure relates to a solid electrolyte, a method forproducing a solid electrolyte, and a composite body.

2. Related Art

As a power supply for many electrical apparatuses such as portableinformation apparatuses, a lithium battery (including a primary batteryand a secondary battery) has been used. Above all, as a lithium batterythat achieves both a high energy density and safety, an all-solid-statelithium battery using a solid electrolyte for lithium conduction betweenpositive and negative electrodes has been proposed (see, for example,JP-A-2009-215130 (Patent Document 1).

A solid electrolyte can conduct lithium ions without using an organicelectrolyte solution, and leakage of an electrolyte solution orvolatilization of an electrolyte solution due to drive heat generation,or the like does not occur, and therefore, it has been attractingattention as a highly safe material.

As a solid electrolyte to be used in such an all-solid-state lithiumbattery, an oxide-based solid electrolyte having a high lithium ionconduction property, an excellent insulation property, and high chemicalstability has been widely known. As such an oxide, a lithium lanthanumzirconate-based material has a remarkably high lithium ion conductivity,and application thereof to a battery has been expected.

When such a solid electrolyte is solid electrolyte particles in aparticulate shape, the solid electrolyte is often molded according to adesired shape by compression molding. However, the solid electrolyteparticles are very hard, and therefore, in the obtained molded product,the contact between the solid electrolyte particles is not sufficientand the grain boundary resistance becomes high, and thus, the lithiumion conductivity is likely to be low.

As a method for reducing the grain boundary resistance, a method offusing solid electrolyte particles by sintering at a high temperature of1000° C. or higher after compression molding the particles is known.However, in such a method, the formulation is likely to be changed dueto the high temperature, and it is difficult to produce a solidelectrolyte molded body having desired physical properties.

Therefore, there has been an attempt to form a material suitable forsintering at a low temperature by substituting some elements in lithiumlanthanum zirconate.

However, a solid electrolyte capable of obtaining a solid electrolytemolded body having a sufficiently low grain boundary resistance at asufficiently low firing temperature has not yet been obtained.

SUMMARY

The present disclosure has been made for solving the above problem andcan be realized as the following application examples.

A solid electrolyte according to an application example of the presentdisclosure is represented by the following compositional formula (1).

Li_(7-2x-z)La₃(Zr_(2-x-z)W_(x)M_(z))O₁₂  (1)

In the formula (1), x and z satisfy 0.10≤x≤0.60 and 0.00<z≤0.25, and Mis at least one type of element selected from the group consisting ofNb, Ta, and Sb.

Further, a method for producing a solid electrolyte according to anapplication example of the present disclosure includes: a mixing step ofmixing multiple types of raw materials containing metal elementsincluded in the following compositional formula (1), thereby obtaining amixture; a first heating step of subjecting the mixture to a firstheating treatment thereby forming a calcined body; and a second heatingstep of subjecting the calcined body to a second heating treatmentthereby forming a crystalline solid electrolyte represented by thefollowing compositional formula (1).

Li_(7-2x-z)La₃(Zr_(2-x-z)W_(x)M_(z))O₁₂  (1)

In the formula (1), x and z satisfy 0.10≤x≤0.60 and 0.00<z≤0.25, and Mis at least one type of element selected from the group consisting ofNb, Ta, and Sb.

Further, a composite body according to an application example of thepresent disclosure includes: an active material; and the solidelectrolyte of the present disclosure that coats a part of a surface ofthe active material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view schematically showing aconfiguration of a lithium-ion battery as a secondary battery of a firstembodiment.

FIG. 2 is a schematic perspective view schematically showing aconfiguration of a lithium-ion battery as a secondary battery of asecond embodiment.

FIG. 3 is a schematic cross-sectional view schematically showing astructure of the lithium-ion battery as the secondary battery of thesecond embodiment.

FIG. 4 is a schematic perspective view schematically showing aconfiguration of a lithium-ion battery as a secondary battery of a thirdembodiment.

FIG. 5 is a schematic cross-sectional view schematically showing astructure of the lithium-ion battery as the secondary battery of thethird embodiment.

FIG. 6 is a schematic perspective view schematically showing aconfiguration of a lithium-ion battery as a secondary battery of afourth embodiment.

FIG. 7 is a schematic cross-sectional view schematically showing astructure of the lithium-ion battery as the secondary battery of thefourth embodiment.

FIG. 8 is a flowchart showing a method for producing the lithium-ionbattery as the secondary battery of the first embodiment.

FIG. 9 is a schematic view schematically showing the method forproducing the lithium-ion battery as the secondary battery of the firstembodiment.

FIG. 10 is a schematic view schematically showing the method forproducing the lithium-ion battery as the secondary battery of the firstembodiment.

FIG. 11 is a schematic cross-sectional view schematically showinganother method for forming a solid electrolyte layer.

FIG. 12 is a flowchart showing a method for producing the lithium-ionbattery as the secondary battery of the second embodiment.

FIG. 13 is a schematic view schematically showing the method forproducing the lithium-ion battery as the secondary battery of the secondembodiment.

FIG. 14 is a schematic view schematically showing the method forproducing the lithium-ion battery as the secondary battery of the secondembodiment.

FIG. 15 is a flowchart showing a method for producing the lithium-ionbattery as the secondary battery of the third embodiment.

FIG. 16 is a schematic view schematically showing the method forproducing the lithium-ion battery as the secondary battery of the thirdembodiment.

FIG. 17 is a schematic view schematically showing the method forproducing the lithium-ion battery as the secondary battery of the thirdembodiment.

FIG. 18 is a flowchart showing a method for producing the lithium-ionbattery as the secondary battery of the fourth embodiment.

FIG. 19 is a schematic view schematically showing the method forproducing the lithium-ion battery as the secondary battery of the fourthembodiment.

FIG. 20 is a view schematically showing a sweep potential-responsecurrent graph obtained by CV measurement.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, preferred embodiments of the present disclosure will bedescribed in detail.

[1] Solid Electrolyte

First, a solid electrolyte according to the present disclosure will bedescribed.

The solid electrolyte according to the present disclosure is representedby the following compositional formula (1).

Li_(7-2x-z)La₃(Zr_(2-x-z)W_(x)M_(z))O₁₂  (1)

In the formula (1), x and z satisfy 0.10≤x≤0.60 and 0.00<z≤0.25, and Mis at least one type of element selected from the group consisting ofNb, Ta, and Sb.

By satisfying such conditions, a solid electrolyte that has an excellentbulk lithium ion conductivity, and is also capable of obtaining a solidelectrolyte molded body having a sufficiently low grain boundaryresistance at a sufficiently low firing temperature can be provided.Further, a solid electrolyte in the related art has a problem that when,for example, the solid electrolyte is co-fired with an active materialsuch as lithium cobalt oxide, mutual diffusion of elements in therespective materials occurs to decrease the lithium ion conductivity,however, in the solid electrolyte according to the present disclosure,even when the solid electrolyte is co-fired with an active material suchas lithium cobalt oxide, the occurrence of the problem that mutualdiffusion of elements in the respective materials occurs to decrease thelithium ion conductivity can be effectively suppressed.

On the other hand, when the conditions as described above are notsatisfied, an excellent effect as described above is not obtained.

For example, when a solid electrolyte does not contain W, it becomesdifficult to make the bulk lithium ion conductivity sufficientlyexcellent, and also it becomes difficult to obtain a solid electrolytemolded body having a sufficiently low grain boundary resistance at asufficiently low firing temperature.

Further, when a solid electrolyte does not contain the M, it becomesdifficult to make the bulk lithium ion conductivity sufficientlyexcellent, and also it becomes difficult to obtain a solid electrolytemolded body having a sufficiently low grain boundary resistance at asufficiently low firing temperature.

Further, even if a solid electrolyte is a lithium lanthanumzirconate-based material containing W and the M, when the content of Win the solid electrolyte is too low, in other words, when the value ofthe x is too small, it becomes difficult to make the bulk lithium ionconductivity sufficiently excellent, and also it becomes difficult toobtain a solid electrolyte molded body having a sufficiently low grainboundary resistance at a sufficiently low firing temperature.

Further, even if a solid electrolyte is a lithium lanthanumzirconate-based material containing W and the M, when the content of Win the solid electrolyte is too high, in other words, when the value ofthe x is too large, it becomes difficult to make the bulk lithium ionconductivity sufficiently excellent, and also it becomes difficult toobtain a solid electrolyte molded body having a sufficiently low grainboundary resistance at a sufficiently low firing temperature.

Further, even if a solid electrolyte is a lithium lanthanumzirconate-based material containing W and the M, when the content of theM in the solid electrolyte is too high, in other words, when the valueof the z is too large, it becomes difficult to make the bulk lithium ionconductivity sufficiently excellent, and also it becomes difficult toobtain a solid electrolyte molded body having a sufficiently low grainboundary resistance at a sufficiently low firing temperature.

As described above, in the compositional formula (1), x need onlysatisfy the condition: 0.10≤x≤0.60, but preferably satisfies thecondition: 0.12≤x≤0.65, more preferably satisfies the condition:0.15≤x≤0.50, and further more preferably satisfies the condition:0.20≤x≤0.40.

According to this, the above-mentioned effect is more remarkablyexhibited.

As described above, in the compositional formula (1), z need onlysatisfy the condition: 0.00<z≤0.25, but preferably satisfies thecondition: 0.03≤z≤0.22, more preferably satisfies the condition:0.05≤z≤0.20, and further more preferably satisfies the condition:0.08≤z≤0.18.

According to this, the above-mentioned effect is more remarkablyexhibited.

In the solid electrolyte, Li is mainly present at C site and aninterstitial position in a garnet-type lithium ion conductorLi₇La₃Zr₂O₁₂ that is a basic structure, and contributes to the lithiumion conduction property.

In the solid electrolyte, La mainly constitutes a garnet-type lithiumion conductor Li₇La₃Zr₂O₁₂ that is a basic structure, and occupies Asite as La³⁺.

In the solid electrolyte, Zr mainly constitutes a garnet-type lithiumion conductor Li₇La₃Zr₂O₁₂ that is a basic structure, and occupies Bsite as Zr⁴⁺.

In the solid electrolyte, W mainly exhibits a function of lowering thetetragonal-cubic transition temperature and the melting point ascompared with a case where W is not contained.

In the solid electrolyte, the M mainly exhibits a function of loweringthe tetragonal-cubic transition temperature and the melting point ascompared with a case where the M is not contained, and imparting a highLi conduction property since an oxide of such M has a high permittivity.

Above all, when the M contains at least Nb, the tetragonal-cubictransition temperature and the melting point are lowered as comparedwith a case where Nb is not contained, and since an oxide of Nb has ahigh permittivity, an effect of imparting a high Li conduction propertyis obtained.

Further, when the M contains at least Ta, the tetragonal-cubictransition temperature and the melting point are lowered as comparedwith a case where Ta is not contained, and since an oxide of Ta has ahigh permittivity, a high Li conduction property is imparted, andfurther, since an oxide of Ta is hardly crystallized, the occurrence ofa grain boundary is likely to be more effectively suppressed.

Further, when the M contains at least Sb, the tetragonal-cubictransition temperature and the melting point are lowered as comparedwith a case where Sb is not contained, and since an oxide of Sb has ahigh permittivity, an effect of imparting a high Li conduction propertyis obtained.

In particular, when the M contains a combination of Nb and Ta, W ispresent much in a crystal bulk, and Nb and Ta are present much in agrain boundary portion. In particular, an oxide of Ta is hardlycrystallized, and therefore, amorphization is caused at grain boundariesdue to the presence of much Ta at grain boundaries, so that theelectrolyte is in a state of being free from grain boundaries, and thegeneration of lithium dendrites is more effectively suppressed.

Further, when the M contains a combination of Sb and Ta, W is presentmuch in a crystal bulk, and Sb and Ta are present much in a grainboundary portion. In particular, an oxide of Ta is hardly crystallized,and therefore, amorphization is caused at grain boundaries due to thepresence of much Ta at grain boundaries, so that the electrolyte is in astate of being free from grain boundaries, and the generation of lithiumdendrites is more effectively suppressed.

When the M contains at least Nb, the ratio of Nb to the entire M ispreferably 20 at % or more and 100 at % or less, more preferably 40 at %or more and 100 at % or less, and further more preferably 50 at % ormore and 100 at % or less.

According to this, the tetragonal-cubic transition temperature and themelting point are lowered, and since an oxide of Nb has a highpermittivity, an effect of imparting a high Li conduction property ismore remarkably obtained.

When the M contains at least Ta, the ratio of Ta to the entire M ispreferably 2 at % or more and 100 at % or less, more preferably 5 at %or more and 100 at % or less, and further more preferably 10 at % ormore and 100 at % or less.

According to this, the tetragonal-cubic transition temperature and themelting point are lowered, and since an oxide of Ta has a highpermittivity, a high Li conduction property is imparted, and further,since an oxide of Ta is hardly crystallized, the occurrence of a grainboundary is likely to be more effectively suppressed.

When the M contains at least Sb, the ratio of Sb to the entire M ispreferably 20 at % or more and 100 at % or less, more preferably 40 at %or more and 100 at % or less, and further more preferably 50 at % ormore and 100 at % or less.

According to this, the tetragonal-cubic transition temperature and themelting point are lowered, and since an oxide of Sb has a highpermittivity, an effect of imparting a high Li conduction property ismore remarkably obtained.

The solid electrolyte according to the present disclosure may containanother element in addition to the elements constituting thecompositional formula (1), that is, an element other than Li, La, Zr, W,Nb, Ta, Sb, and O as long as the amount thereof is a trace amount. Theanother element may be one type or two or more types.

The content of the another element contained in the solid electrolyteaccording to the present disclosure is preferably 100 ppm or less, andmore preferably 50 ppm or less.

When two or more types of elements are contained as the another element,the sum of the contents of these elements shall be adopted as thecontent of the another element.

The crystal phase of the solid electrolyte according to the presentdisclosure is generally a cubic garnet-type crystal.

The solid electrolyte according to the present disclosure may be, forexample, used by itself or in combination with another component. Morespecifically, the solid electrolyte according to the present disclosuremay be, for example, used as a substance that constitutes a solidelectrolyte layer as described later in a battery by itself, or may be asubstance that constitutes a solid electrolyte layer in a mixed statewith another solid electrolyte. In addition, for example, the solidelectrolyte according to the present disclosure may be a substance thatconstitutes a positive electrode layer in a mixed state with a positiveelectrode active material, or may be a substance that constitutes anegative electrode layer in a mixed state with a negative electrodeactive material.

[2] Method for Producing Solid Electrolyte

Next, a method for producing a solid electrolyte according to thepresent disclosure will be described.

The method for producing a solid electrolyte according to the presentdisclosure includes a mixing step of mixing multiple types of rawmaterials containing metal elements included in the compositionalformula (1), thereby obtaining a mixture, a first heating step ofsubjecting the mixture to a first heating treatment thereby forming acalcined body, and a second heating step of subjecting the calcined bodyto a second heating treatment thereby forming a crystalline solidelectrolyte represented by the compositional formula (1).

According to this, a method for producing a solid electrolyte that hasan excellent bulk lithium ion conductivity, and is also capable ofobtaining a solid electrolyte molded body having a sufficiently lowgrain boundary resistance at a sufficiently low firing temperature canbe provided. Further, a solid electrolyte in the related art has aproblem that when, for example, the solid electrolyte is co-fired withan active material such as lithium cobalt oxide, mutual diffusion ofelements in the respective materials occurs to decrease the lithium ionconductivity, however, in the method for producing a solid electrolyteaccording to the present disclosure, even when it is applied toco-firing with an active material such as lithium cobalt oxide, theoccurrence of the problem that mutual diffusion of elements in therespective materials occurs to decrease the lithium ion conductivity canbe effectively suppressed.

[2-1] Mixing Step

In the mixing step, a mixture is obtained by mixing multiple types ofraw materials containing metal elements included in the compositionalformula (1).

In this step, two or more types of metal elements among the metalelements included in the compositional formula (1) need only becontained in the mixture obtained by mixing multiple types of rawmaterials as a whole.

Further, at least one type of the multiple types of raw materials to beused in this step may be an oxoacid compound containing an oxoaniontogether with a metal ion.

According to this, by a heat treatment at a relatively low temperaturefor a relatively short time, a solid electrolyte having a desiredproperty can be stably formed. More specifically, by using an oxoacidcompound in this step, a calcined body can be obtained as a materialcontaining an oxide that is different from a solid electrolyte to befinally obtained and an oxoacid compound in the later step. As a result,the melting point of the oxide is lowered, and a close contact interfacewith an adherend can be formed while promoting the crystal growth in afiring treatment that is a heat treatment at a relatively lowtemperature for a relatively short time.

The oxoanion constituting the oxoacid compound does not contain a metalelement, and for example, a halogen oxoacid, a borate ion, a carbonateion, an orthocarbonate ion, a carboxylate ion, a silicate ion, a nitriteion, a nitrate ion, a phosphite ion, a phosphate ion, an arsenate ion, asulfite ion, a sulfate ion, a sulfonate ion, a sulfinate ion, and thelike are exemplified. As the halogen oxoacid, for example, ahypochlorous ion, a chlorite ion, a chlorate ion, a perchlorate ion, ahypobromite ion, a bromite ion, a bromate ion, a perbromate ion, ahypoiodite ion, an iodite ion, an iodate ion, a periodate ion, and thelike are exemplified. Above all, the oxoacid compound preferablycontains at least one of a nitrate ion and a sulfate ion as theoxoanion, and more preferably contains a nitrate ion.

According to this, the melting point of the metal oxide contained in thecalcined body obtained in the first heating step that will be describedin detail later is more favorably lowered, and the crystal growth of alithium-containing composite oxide can be more effectively promoted. Asa result, even when the second heating step that will be described indetail later is performed at a lower temperature for a shorter time, asolid electrolyte having a particularly excellent ion conductionproperty can be favorably obtained. In the following description, ametal oxide contained in the calcined body obtained in the first heatingstep is also referred to as “precursor oxide”.

As the raw materials containing metal elements, for example, a simplesubstance metal or an alloy may be used, or a compound in which a metalelement contained in a molecule is only one type may be used, or acompound containing multiple types of metal elements in a molecule maybe used.

As a lithium compound that is a raw material containing Li, for example,a lithium metal salt, a lithium alkoxide, and the like are exemplified,and it is possible to use one type or two or more types in combinationamong these. Examples of the lithium metal salt include lithiumchloride, lithium nitrate, lithium sulfate, lithium acetate, lithiumhydroxide, lithium carbonate, and (2,4-pentanedionato)lithium. Examplesof the lithium alkoxide include lithium methoxide, lithium ethoxide,lithium propoxide, lithium isopropoxide, lithium butoxide, lithiumisobutoxide, lithium sec-butoxide, lithium tert-butoxide, anddipivaloylmethanato lithium. Above all, the lithium compound ispreferably one type or two or more types selected from the groupconsisting of lithium nitrate, lithium sulfate, and(2,4-pentanedionato)lithium. As the raw material containing Li, ahydrate may be used.

As a lanthanum compound that is a raw material containing La, forexample, a lanthanum metal salt, a lanthanum alkoxide, lanthanumhydroxide, and the like are exemplified, and it is possible to use onetype or two or more types in combination among these. Examples of thelanthanum metal salt include lanthanum chloride, lanthanum nitrate,lanthanum sulfate, lanthanum acetate, andtris(2,4-pentanedionato)lanthanum. Examples of the lanthanum alkoxideinclude lanthanum trimethoxide, lanthanum triethoxide, lanthanumtripropoxide, lanthanum triisopropoxide, lanthanum tributoxide,lanthanum triisobutoxide, lanthanum tri-sec-butoxide, lanthanumtri-tert-butoxide, and dipivaloylmethanato lanthanum. Above all, thelanthanum compound is preferably at least one type selected from thegroup consisting of lanthanum nitrate,tris(2,4-pentanedionato)lanthanum, and lanthanum hydroxide. As the rawmaterial containing La, a hydrate may be used.

As a zirconium compound that is a raw material containing Zr, forexample, a zirconium metal salt, a zirconium alkoxide, and the like areexemplified, and it is possible to use one type or two or more types incombination among these. Examples of the zirconium metal salt includezirconium chloride, zirconium oxychloride, zirconium oxynitrate,zirconium oxysulfate, zirconium oxyacetate, and zirconium acetate.Examples of the zirconium alkoxide include zirconium tetramethoxide,zirconium tetraethoxide, zirconium tetrapropoxide, zirconiumtetraisopropoxide, zirconium tetra-n-butoxide, zirconiumtetraisobutoxide, zirconium tetra-sec-butoxide, zirconiumtetra-tert-butoxide, and dipivaloylmethanato zirconium. Above all, asthe zirconium compound, zirconium tetra-n-butoxide is preferred. As theraw material containing Zr, a hydrate may be used.

As a tungsten compound that is a raw material containing W, for example,a tungsten metal salt, a tungsten alkoxide, and the like areexemplified, and it is possible to use one type or two or more types incombination among these. Examples of the tungsten metal salt includetungsten chloride and tungsten oxychloride. Examples of the tungstenalkoxide include tungsten ethoxide such as tungsten pentaethoxide, andtungsten isopropoxide. Above all, as the tungsten compound, tungstenpentaethoxide is preferred. As the raw material containing W, a hydratemay be used.

As a niobium compound that is a raw material containing Nb, for example,a niobium metal salt, a niobium alkoxide, niobium acetylacetone, and thelike are exemplified, and it is possible to use one type or two or moretypes in combination among these. Examples of the niobium metal saltinclude niobium chloride, niobium oxychloride, and niobium oxalate.Examples of the niobium alkoxide include niobium ethoxide such asniobium pentaethoxide, niobium propoxide, niobium isopropoxide, andniobium sec-butoxide. Above all, as the niobium compound, niobiumpentaethoxide is preferred. As the raw material containing Nb, a hydratemay be used.

As a tantalum compound that is a raw material containing Ta, forexample, a tantalum metal salt, a tantalum alkoxide, and the like areexemplified, and it is possible to use one type or two or more types incombination among these. Examples of the tantalum metal salt includetantalum chloride and tantalum bromide. Examples of the tantalumalkoxide include tantalum pentamethoxide, tantalum pentaethoxide,tantalum pentaisopropoxide, tantalum penta-n-propoxide, tantalumpentaisobutoxide, tantalum penta-n-butoxide, tantalumpenta-sec-butoxide, and tantalum penta-tert-butoxide. Above all, as thetantalum compound, tantalum pentaethoxide is preferred. As the rawmaterial containing Ta, a hydrate may be used.

As an antimony compound that is a raw material containing Sb, forexample, an antimony metal salt, an antimony alkoxide, and the like areexemplified, and it is possible to use one type or two or more types incombination among these. Examples of the antimony metal salt includeantimony bromide, antimony chloride, antimony fluoride, and antimonysulfate. Examples of the antimony alkoxide include antimonytrimethoxide, antimony triethoxide, antimony triisopropoxide, antimonytri-n-propoxide, antimony triisobutoxide, and antimony tri-n-butoxide.Above all, as the antimony compound, antimony triisobutoxide andantimony tri-n-butoxide are preferred. As the raw material containingSb, a hydrate may be used.

In the preparation of the mixture, a solvent may be used.

According to this, the multiple types of raw materials containing metalelements included in the compositional formula (1) can be more favorablymixed.

The solvent is not particularly limited, and for example, various typesof organic solvents can be used, however, more specifically, forexample, an alcohol, a glycol, a ketone, an ester, an ether, an organicacid, an aromatic, an amide, and the like are exemplified, and one typeor a mixed solvent that is a combination of two or more types selectedfrom these can be used. Examples of the alcohol include methyl alcohol,ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol,allyl alcohol, and 2-n-butoxyethanol. Examples of the glycol includeethylene glycol, propylene glycol, butylene glycol, hexylene glycol,pentanediol, hexanediol, heptanediol, and dipropylene glycol. Examplesof the ketone include dimethyl ketone, methyl ethyl ketone, methylpropyl ketone, and methyl isobutyl ketone. Examples of the ester includemethyl formate, ethyl formate, methyl acetate, and methyl acetoacetate.Examples of the ether include diethylene glycol monomethyl ether,diethylene glycol monoethyl ether, diethylene glycol dimethyl ether,ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, anddipropylene glycol monomethyl ether. Examples of the organic acidinclude formic acid, acetic acid, 2-ethylbutyric acid, and propionicacid. Examples of the aromatic include toluene, o-xylene, and p-xylene.Examples of the amide include formamide, N,N-dimethylformamide,N,N-diethylformamide, dimethylacetamide, and N-methylpyrrolidone. Aboveall, the solvent is preferably at least one of 2-n-butoxyethanol andpropionic acid.

When a solvent is used in the preparation of the mixture, the solventmay be at least partially removed prior to the first heating step thatwill be described in detail later.

The removal of the solvent prior to the first heating step can beperformed by, for example, heating the mixture, placing the mixture in areduced pressure atmosphere, or placing the mixture under normaltemperature and normal pressure. By at least partially removing thesolvent, the mixture can be favorably gelled. Note that the “normaltemperature and normal pressure” as used herein refers to 25° C. and 1atm.

Hereinafter, when the removal of the solvent is performed by a heatingtreatment, the heating treatment is also referred to as “preheatingtreatment”.

The conditions of the preheating treatment depend on the boiling pointor the vapor pressure of the solvent or the like, but the heatingtemperature in the preheating treatment is preferably 50° C. or higherand 250° C. or lower, more preferably 60° C. or higher and 230° C. orlower, and further more preferably 80° C. or higher and 200° C. orlower. During the preheating treatment, the heating temperature may bechanged. For example, the preheating treatment may include a first stagein which a heat treatment is performed while maintaining a relativelylow temperature, and a second stage in which the temperature is raisedafter the first stage, and a heat treatment at a relatively hightemperature is performed. In such a case, it is preferred that thehighest temperature in the preheating treatment falls within theabove-mentioned range.

Further, the heating time in the preheating treatment is preferably 10minutes or more and 180 minutes or less, more preferably 20 minutes ormore and 120 minutes or less, and further more preferably 30 minutes ormore and 60 minutes or less.

The preheating treatment may be performed in any atmosphere, and may beperformed in an oxidizing atmosphere such as in the air or in an oxygengas atmosphere, or may be performed in a non-oxidizing atmosphere of aninert gas such as nitrogen gas, helium gas, or argon gas, or the like.Further, the preheating treatment may be performed under reducedpressure or vacuum, or under pressure.

Further, during the preheating treatment, the atmosphere may bemaintained under substantially the same conditions, or may be changed todifferent conditions. For example, the preheating treatment may includea first stage in which a heat treatment is performed in a normalpressure environment and a second stage in which a heat treatment isperformed in a reduced pressure environment after the first stage.

[2-2] First Heating Step

In the first heating step, the mixture obtained in the mixing step, forexample, the gelled mixture is subjected to a first heating treatment,thereby forming a calcined body.

In particular, when an oxoacid compound is used for part of the rawmaterials, a calcined body containing a precursor oxide that is an oxidedifferent from the solid electrolyte to be finally obtained, and theoxoacid compound is obtained.

The heating temperature in the first heating step is not particularlylimited, but is preferably 500° C. or higher and 650° C. or lower, morepreferably 510° C. or higher and 650° C. or lower, and further morepreferably 520° C. or higher and 600° C. or lower.

According to this, undesirable vaporization of metal elements toconstitute the solid electrolyte to be finally obtained, particularlyvaporization of Li that easily vaporizes among the metal materials, orthe like can be more effectively prevented, and the formulation of thesolid electrolyte to be finally obtained can be more strictlycontrolled, and also the solid electrolyte can be more efficientlyproduced.

During the first heating step, the heating temperature may be changed.For example, the first heating step may include a first stage in which aheat treatment is performed while maintaining a relatively lowtemperature, and a second stage in which the temperature is raised afterthe first stage, and a heat treatment at a relatively high temperatureis performed. In such a case, it is preferred that the highesttemperature in the first heating step falls within the above-mentionedrange.

Further, the heating time in the first heating step, particularly theheating time when the heating temperature is 500° C. or higher and 650°C. or lower is preferably 5 minutes or more and 180 minutes or less,more preferably 10 minutes or more and 120 minutes or less, and furthermore preferably 15 minutes or more and 90 minutes or less.

The first heating step may be performed in any atmosphere, and may beperformed in an oxidizing atmosphere such as in the air or in an oxygengas atmosphere, or may be performed in a non-oxidizing atmosphere of aninert gas such as nitrogen gas, helium gas, or argon gas, or the like.Further, the first heating step may be performed under reduced pressureor vacuum, or under pressure. In particular, the first heating step ispreferably performed in an oxidizing atmosphere.

Further, during the first heating step, the atmosphere may be maintainedunder substantially the same conditions, or may be changed to differentconditions. For example, the first heating step may include a firststage in which a heat treatment is performed in an inert gas atmosphereand a second stage in which a heat treatment is performed in anoxidizing atmosphere after the first stage.

The calcined body obtained as described above generally contains aprecursor oxide having a crystal phase which is different from that ofthe solid electrolyte to be finally obtained, that is, the solidelectrolyte represented by the compositional formula (1) at normaltemperature and normal pressure. In this specification, the “different”in terms of crystal phase is a broad concept not only including that thetype of crystal phase is not the same, but also including that even ifthe type is the same, at least one lattice constant is different, or thelike.

As the crystal phase of the precursor oxide, for example, cubic crystalssuch as a pyrochlore-type crystal, a perovskite structure, a rocksalt-type structure, a diamond structure, a fluorite-type structure, anda spinel-type structure, orthorhombic crystals such as a ramsdellitetype, a trigonal crystal such as a corundum type, and the like areexemplified, however, the crystal phase is preferably a pyrochlore-typecrystal.

According to this, even when the conditions in the second heating stepdescribed later are set to a lower temperature and a shorter time, asolid electrolyte having a particularly excellent ion conductionproperty can be favorably obtained.

The crystal grain diameter of the precursor oxide is not particularlylimited, but is preferably 10 nm or more and 200 nm or less, morepreferably 15 nm or more and 180 nm or less, and further more preferably20 nm or more and 160 nm or less.

According to this, due to a so-called Gibbs-Thomson effect that is aphenomenon of lowering the melting point with an increase in surfaceenergy, the melting temperature of the precursor oxide or the firingtemperature in the second heating step can be further lowered. Further,this is also advantageous to the improvement of joining of the solidelectrolyte to be produced using the method according to the presentdisclosure to a heterogeneous material or the reduction of the defectdensity.

The precursor oxide is preferably constituted by a substantially singlecrystal phase.

According to this, the precursor oxide undergoes crystal phasetransition substantially once when producing the solid electrolyte usingthe method according to the present disclosure, that is, when generatinga high-temperature crystal phase, and therefore, segregation of elementsaccompanying the crystal phase transition or generation of a contaminantcrystal by thermal decomposition is suppressed, so that variousproperties of the solid electrolyte to be produced are further improved.

In a case where only one exothermic peak is observed within a range of300° C. or higher and 1,000° C. or lower when measurement is performedby TG-DTA at a temperature raising rate of 10° C./min for the calcinedbody obtained in the first heating step, it can be determined that “itis constituted by a substantially single crystal phase”.

The formulation of the precursor oxide is not particularly limited,however, the precursor oxide is preferably a composite oxide. Inparticular, the precursor oxide is preferably a composite oxidecontaining Li and La.

According to this, even when a heat treatment in the second heating stepdescribed later is performed at a lower temperature for a shorter time,a solid electrolyte having a particularly excellent ion conductionproperty can be favorably obtained. In addition, for example, in anall-solid-state secondary battery, the adhesion of the solid electrolyteto be formed to a positive electrode active material or a negativeelectrode active material can be made more excellent, and a compositematerial can be formed so as to have a more favorable close contactinterface, and thus, the properties and reliability of theall-solid-state secondary battery can be made more excellent.

Further, in the calcined body obtained as described above, generally,almost all the solvent used in the production process is removed,however, a portion of the solvent may remain. However, the content ofthe solvent in the calcined body is preferably 1.0 mass % or less, andmore preferably 0.1 mass % or less.

[2-3] Second Heating Step

In the second heating step, the calcined body obtained in the firstheating step is subjected to a second heating treatment, thereby forminga crystalline solid electrolyte represented by the compositional formula(1).

In particular, when the calcined body obtained in the first heating stepcontains an oxoacid compound, the melting point of the precursor oxideis favorably lowered, and the crystal growth of a lithium-containingcomposite oxide can be promoted, and by a heat treatment at a relativelylow temperature for a relatively short time, a solid electrolyte havinga desired property can be stably formed. In addition, the adhesionbetween the solid electrolyte to be formed and an adherend can be madefavorable.

The second heating step may be performed after mixing another componentin the calcined body described above.

For example, the second heating step may be performed for a mixture ofthe calcined body with an oxoacid compound.

Even in such a case, the same effect as described above is obtained.

Here, as a specific example of the oxoacid compound that can be mixedwith the calcined body, the oxoacid compound contained in the metalcompound exemplified as the raw material of the mixture described above,or the like is exemplified.

In the second heating step, the calcined body may be subjected to theheating step in a state of being mixed with an active material such as apositive electrode active material or a negative electrode activematerial.

According to this, an electrode such as a positive electrode or anegative electrode can be favorably produced in a state where the solidelectrolyte is contained together with the active material. The positiveelectrode active material and the negative electrode active materialwill be described in detail later.

A composition to be subjected to the second heating step containsmultiple types of metal elements as the constituent elements of thesolid electrolyte as a whole, and generally, the ratio of the contentsthereof corresponds to the content ratio of each metal element in theformulation of the target solid electrolyte, that is, the compositionalformula (1).

When the composition to be subjected to this step contains an oxoacidcompound, the content of the oxoacid compound in the composition is notparticularly limited, but is preferably 0.1 mass % or more and 20 mass %or less, more preferably 1.5 mass % or more and 15 mass % or less, andfurther more preferably 2.0 mass % or more and 10 mass % or less.

According to this, a heat treatment in the second heating step can befavorably performed at a lower temperature for a shorter time while morereliably preventing the oxoacid compound from undesirably remaining inthe solid electrolyte to be finally obtained, and the ion conductionproperty of the solid electrolyte to be obtained can be madeparticularly excellent.

The content of the precursor oxide in the composition to be subjected tothis step is not particularly limited, but is preferably 35 mass % ormore and 85 mass % or less, and more preferably 45 mass % or more and 90mass % or less.

When the content of the precursor oxide in the composition to besubjected to this step is represented by XP [mass %] and the content ofthe oxoacid compound in the composition to be subjected to this step isrepresented by XO [mass %], it is preferred to satisfy a relationship:0.013≤XO/XP≤0.58, it is more preferred to satisfy a relationship:0.023≤XO/XP≤0.34, and it is further more preferred to satisfy arelationship: 0.03≤XO/XP≤0.19.

According to this, a heat treatment in the second heating step can befavorably performed at a lower temperature for a shorter time while morereliably preventing the oxoacid compound from undesirably remaining inthe solid electrolyte to be finally obtained, and the ion conductionproperty of the solid electrolyte to be obtained can be madeparticularly excellent.

The heating temperature in the second heating step is not particularlylimited, but is generally a higher temperature than the heatingtemperature in the first heating step, and is preferably 800° C. orhigher and 1000° C. or lower, more preferably 810° C. or higher and 980°C. or lower, and further more preferably 820° C. or higher and 950° C.or lower.

According to this, by a heat treatment at a relatively low temperaturefor a relatively short time, a solid electrolyte having a desiredproperty can be stably formed. Further, since a solid electrolyte can beproduced by a heat treatment at a relatively low temperature for arelatively short time, for example, the productivity of the solidelectrolyte or an all-solid-state battery including the solidelectrolyte can be made more excellent, and also from the viewpoint ofenergy saving, such a heat treatment is preferred.

During the second heating step, the heating temperature may be changed.For example, the second heating step may include a first stage in whicha heat treatment is performed while maintaining a relatively lowtemperature, and a second stage in which the temperature is raised afterthe first stage, and a heat treatment at a relatively high temperatureis performed. In such a case, it is preferred that the highesttemperature in the second heating step falls within the above-mentionedrange.

The heating time in the second heating step, particularly the heatingtime when the heating temperature is 800° C. or higher and 1000° C. orlower is, but not particularly limited to, preferably 5 minutes or moreand 600 minutes or less, more preferably 10 minutes or more and 540minutes or less, and further more preferably 15 minutes or more and 500minutes or less.

According to this, by a heat treatment at a relatively low temperaturefor a relatively short time, a solid electrolyte having a desiredproperty can be stably formed. Further, since the solid electrolyte canbe produced by a heat treatment at a relatively low temperature for arelatively short time, for example, the productivity of the solidelectrolyte or an all-solid-state battery including the solidelectrolyte can be made more excellent, and also from the viewpoint ofenergy saving, such a heat treatment is preferred.

The second heating step may be performed in any atmosphere, and may beperformed in an oxidizing atmosphere such as in the air or in an oxygengas atmosphere, or may be performed in a non-oxidizing atmosphere of aninert gas such as nitrogen gas, helium gas, or argon gas, or the like.Further, the heating step may be performed under reduced pressure orvacuum, or under pressure. In particular, the second heating step ispreferably performed in an oxidizing atmosphere.

Further, during the second heating step, the atmosphere may bemaintained under substantially the same conditions, or may be changed todifferent conditions.

Even when the oxoacid compound is used as a raw material, the solidelectrolyte obtained as described above generally does not substantiallycontain the oxoacid compound. More specifically, the content of theoxoacid compound in the solid electrolyte to be obtained is generally100 ppm or less, and particularly, it is preferably 50 ppm or less, andmore preferably 10 ppm or less.

According to this, the content of an undesirable impurity in the solidelectrolyte can be suppressed, and the properties and reliability of thesolid electrolyte can be made more excellent.

[3] Composite Body

Next, a composite body according to the present disclosure will bedescribed.

The composite body according to the present disclosure includes anactive material and the solid electrolyte according to the presentdisclosure that coats a part of a surface of the active material.

According to this, a composite body having a sufficiently low grainboundary resistance between the active material and the solidelectrolyte can be provided. Such a composite body can be favorablyapplied to a positive electrode composite material or a negativeelectrode composite material of a secondary battery as described later.As a result, the properties and reliability of the secondary battery asa whole can be made excellent.

Examples of the active material constituting the composite bodyaccording to the present disclosure include a positive electrode activematerial and a negative electrode active material.

As the positive electrode active material, for example, a lithiumcomposite oxide which contains at least Li and is constituted by any oneor more types of elements selected from the group consisting of V, Cr,Mn, Fe, Co, Ni, and Cu, or the like can be used. Examples of such acomposite oxide include LiCoO₂, LiNiO₂, LiMn₂O₄, Li₂Mn₂O₃,LiCr_(0.5)Mn_(0.5)O₂, LiFePO₄, Li₂FeP₂O₇, LiMnPO₄, LiFeBO₃, Li₃V₂(PO₄)₃,Li₂CuO₂, Li₂FeSiO₄, and Li₂MnSiO₄. Further, as the positive electrodeactive material, for example, a fluoride such as LiFeF₃, a boridecomplex compound such as LiBH₄ or Li₄BN₃H₁₀, an iodine complex compoundsuch as a polyvinylpyridine-iodine complex, a nonmetallic compound suchas sulfur, or the like can also be used.

Examples of the negative electrode active material include Nb₂O₅, V₂O₅,TiO₂, In₂O₃, ZnO, SnO₂, NiO, ITO, AZO, GZO, ATO, FTO, and lithiumcomposite oxides such as Li₄TisO₁₂ and Li₂Ti₃O₇. Further, additionalexamples thereof include metals and alloys such as Li, Al, Si, Si—Mn,Si—Co, Si—Ni, Sn, Zn, Sb, Bi, In, and Au, carbon materials, andmaterials obtained by intercalation of lithium ions between layers of acarbon material such as LiC₂₄ and LiC₆.

The composite body according to the present disclosure can be favorablyproduced by, for example, applying the method for producing a solidelectrolyte described in the above [2]. More specifically, for example,the composite body can be favorably produced by firing the mixture ofthe calcined body and the active material described above, that is, bysubjecting the mixture to the second heating treatment.

[4] Secondary Battery

Next, a secondary battery to which the present disclosure is appliedwill be described.

A secondary battery according to the present disclosure includes thesolid electrolyte according to the present disclosure as describedabove, and can be produced by, for example, applying the method forproducing a solid electrolyte according to the present disclosuredescribed above.

Such a secondary battery has excellent charge-discharge characteristics.

[4-1] Secondary Battery of First Embodiment

Hereinafter, a secondary battery according to a first embodiment will bedescribed.

FIG. 1 is a schematic perspective view schematically showing aconfiguration of a lithium-ion battery as the secondary battery of thefirst embodiment.

As shown in FIG. 1, a lithium-ion battery 100 as the secondary batteryincludes a positive electrode 10, and a solid electrolyte layer 20 and anegative electrode 30, which are sequentially stacked on the positiveelectrode 10. The lithium-ion battery further includes a currentcollector 41 in contact with the positive electrode 10 at an oppositeface side of the positive electrode 10 from a face thereof facing thesolid electrolyte layer 20, and includes a current collector 42 incontact with the negative electrode 30 at an opposite face side of thenegative electrode 30 from a face thereof facing the solid electrolytelayer 20. The positive electrode 10, the solid electrolyte layer 20, andthe negative electrode 30 are all constituted by a solid phase, andtherefore, the lithium-ion battery 100 is a chargeable and dischargeableall solid-state secondary battery.

The shape of the lithium-ion battery 100 is not particularly limited,and may be, for example, a polygonal disk shape or the like, but is acircular disk shape in the configuration shown in the drawing. The sizeof the lithium-ion battery 100 is not particularly limited, but forexample, the diameter of the lithium-ion battery 100 is, for example, 10mm or more and 20 mm or less, and the thickness of the lithium-ionbattery 100 is, for example, 0.1 mm or more and 1.0 mm or less.

When the lithium-ion battery 100 is small and thin in this manner,together with the fact that it is chargeable and dischargeable and is anall solid-state battery, it can be favorably used as a power supply of aportable information terminal such as a smartphone. The lithium-ionbattery 100 may be used for a purpose other than the power supply of aportable information terminal as described later.

Hereinafter, the respective configurations of the lithium-ion battery100 will be described.

[4-1-1] Solid Electrolyte Layer

The solid electrolyte layer 20 is constituted by a material includingthe solid electrolyte according to the present disclosure describedabove.

According to this, the ion conductivity of the solid electrolyte layer20 becomes excellent. Further, the adhesion of the solid electrolytelayer 20 to the positive electrode 10 or the negative electrode 30 canbe made excellent. As a result, the properties and reliability of thelithium-ion battery 100 as a whole can be made particularly excellent.

The solid electrolyte layer 20 may contain a component other than thesolid electrolyte according to the present disclosure described above.For example, the solid electrolyte layer 20 may contain another solidelectrolyte together with the solid electrolyte according to the presentdisclosure described above.

However, the content of the solid electrolyte according to the presentdisclosure in the solid electrolyte layer 20 is preferably 80 mass % ormore, more preferably 90 mass % or more, and further more preferably 95mass % or more.

According to this, the effect of the present disclosure as describedabove is more remarkably exhibited.

The thickness of the solid electrolyte layer 20 is not particularlylimited, but is preferably 0.3 μm or more and 1000 μm or less, and morepreferably 0.5 μm or more and 100 μm or less from the viewpoint ofcharge-discharge rate.

Further, from the viewpoint of preventing a short circuit between thepositive electrode 10 and the negative electrode 30 due to a lithiumdendritic crystal body deposited at the negative electrode 30 side, avalue obtained by dividing the measured weight of the solid electrolytelayer 20 by a value obtained by multiplying the apparent volume of thesolid electrolyte layer 20 by the theoretical density of the solidelectrolyte material, that is, the sintered density is preferably set to50% or more, and more preferably set to 90% or more.

As a method for forming the solid electrolyte layer 20, for example, agreen sheet method, a press firing method, a cast firing method, or thelike is exemplified. A specific example of the method for forming thesolid electrolyte layer 20 will be described in detail later. For thepurpose of improving the adhesion of the solid electrolyte layer 20 tothe positive electrode 10 and the negative electrode 30, or improvingthe output or battery capacity of the lithium-ion battery 100 by anincrease in specific surface area, or the like, for example, athree-dimensional pattern structure such as a dimple, trench, or pillarpattern may be formed at a surface of the solid electrolyte layer 20 tocome in contact with the positive electrode 10 or the negative electrode30.

[4-1-2] Positive Electrode

The positive electrode 10 may be any as long as it is constituted by apositive electrode active material that can repeat electrochemicalocclusion and release of lithium ions.

Specifically, as the positive electrode active material constituting thepositive electrode 10, for example, a lithium composite oxide whichcontains at least Li and is constituted by any one or more types ofelements selected from the group consisting of V, Cr, Mn, Fe, Co, Ni,and Cu, or the like can be used. Examples of such a composite oxideinclude LiCoO₂, LiNiO₂, LiMn₂O₄, Li₂Mn₂O₃, LiCr_(0.5)Mn_(0.5)O₂,LiFePO₄, Li₂FeP₂O₇, LiMnPO₄, LiFeBO₃, Li₃V₂(PO₄)₃, Li₂CuO₂, Li₂FeSiO₄,and Li₂MnSiO₄. Further, as the positive electrode active materialconstituting the positive electrode 10, for example, a fluoride such asLiFeF₃, a boride complex compound such as LiBH₄ or Li₄BN₃H₁₀, an iodinecomplex compound such as a polyvinylpyridine-iodine complex, anonmetallic compound such as sulfur, or the like can also be used.

The positive electrode 10 is preferably formed as a thin film at onesurface of the solid electrolyte layer 20 in consideration of anelectric conduction property and an ion diffusion distance.

The thickness of the positive electrode 10 formed of the thin film isnot particularly limited, but is preferably 0.1 μm or more and 500 μm orless, and more preferably 0.3 μm or more and 100 μm or less.

As a method for forming the positive electrode 10, for example, a vaporphase deposition method such as a vacuum vapor deposition method, asputtering method, a CVD method, a PLD method, an ALD method, or anaerosol deposition method, a chemical deposition method using a solutionsuch as a sol-gel method or an MOD method, or the like is exemplified.In addition, for example, fine particles of the positive electrodeactive material are formed into a slurry together with an appropriatebinder, followed by squeegeeing or screen printing, thereby forming acoating film, and then, the coating film may be baked onto the surfaceof the solid electrolyte layer 20 by drying and firing.

[4-1-3] Negative Electrode

The negative electrode 30 may be any as long as it is constituted by aso-called negative electrode active material that repeatselectrochemical occlusion and release of lithium ions at a lowerpotential than the material selected as the positive electrode 10.

Specifically, examples of the negative electrode active materialconstituting the negative electrode 30 include Nb₂O, V₂O₅, TiO₂, In₂O₃,ZnO, SnO₂, NiO, ITO, AZO, GZO, ATO, FTO, and lithium composite oxidessuch as Li₄Ti₅O₁₂ and Li₂Ti₃O₇. Further, additional examples thereofinclude metals and alloys such as Li, Al, Si, Si—Mn, Si—Co, Si—Ni, Sn,Zn, Sb, Bi, In, and Au, carbon materials, and materials obtained byintercalation of lithium ions between layers of a carbon material suchas LiC₂₄ and LiC₆.

The negative electrode 30 is preferably formed as a thin film at onesurface of the solid electrolyte layer 20 in consideration of anelectric conduction property and an ion diffusion distance.

The thickness of the negative electrode 30 formed of the thin film isnot particularly limited, but is preferably 0.1 μm or more and 500 μm orless, and more preferably 0.3 μm or more and 100 μm or less.

As a method for forming the negative electrode 30, for example, a vaporphase deposition method such as a vacuum vapor deposition method, asputtering method, a CVD method, a PLD method, an ALD method, or anaerosol deposition method, a chemical deposition method using a solutionsuch as a sol-gel method or an MOD method, or the like is exemplified.In addition, for example, fine particles of the negative electrodeactive material are formed into a slurry together with an appropriatebinder, followed by squeegeeing or screen printing, thereby forming acoating film, and then, the coating film may be baked onto the surfaceof the solid electrolyte layer 20 by drying and firing.

[4-1-4] Current Collector

The current collectors 41 and 42 are electric conductors provided so asto play a role in transfer of electrons to the positive electrode 10 orthe negative electrode 30. As the current collector, generally, acurrent collector constituted by a material that has a sufficientlysmall electrical resistance, and that does not substantially change theelectric conduction property or the mechanical structure thereof bycharging and discharging is used. Specifically, as the constituentmaterial of the current collector 41 of the positive electrode 10, forexample, Al, Ti, Pt, Au, or the like is used. Further, as theconstituent material of the current collector 42 of the negativeelectrode 30, for example, Cu or the like is favorably used.

The current collectors 41 and 42 are generally provided so that thecontact resistance with the positive electrode 10 and the negativeelectrode 30 becomes small, respectively. Examples of the shape of eachof the current collectors 41 and 42 include a plate shape and a meshshape.

The thickness of each of the current collectors 41 and 42 is notparticularly limited, but is preferably 7 μm or more and 85 μm or less,and more preferably 10 μm or more and 60 μm or less.

In the configuration shown in the drawing, the lithium-ion battery 100includes a pair of current collectors 41 and 42, however, for example,when a plurality of lithium-ion batteries 100 are used by being stackedand electrically coupled to one another in series, the lithium-ionbattery 100 may also be configured to include only the current collector41 of the current collectors 41 and 42.

The lithium-ion battery 100 may be used for any purpose. Examples of anelectronic device to which the lithium-ion battery 100 is applied as apower supply include a personal computer, a digital camera, a cellularphone, a smartphone, a music player, a tablet terminal, a timepiece, asmartwatch, various types of printers such as an inkjet printer, atelevision, a projector, wearable terminals such as a head-up display,wireless headphones, wireless earphones, smart glasses, and ahead-mounted display, a video camera, a videotape recorder, a carnavigation device, a drive recorder, a pager, an electronic notebook, anelectronic dictionary, an electronic translation machine, an electroniccalculator, an electronic gaming device, a toy, a word processor, a workstation, a robot, a television telephone, a television monitor for crimeprevention, electronic binoculars, a POS terminal, a medical device, afish finder, various types of measurement devices, a device for mobileterminal base stations, various types of meters for vehicles, railroadcars, airplanes, helicopters, ships, or the like, a flight simulator,and a network server. Further, the lithium-ion battery 100 may beapplied to, for example, moving objects such as a car and a ship. Morespecifically, it can be favorably applied as, for example, a storagebattery for electric cars, plug-in hybrid cars, hybrid cars, fuel cellcars, or the like. In addition, it can also be applied to, for example,a power supply for household use, a power supply for industrial use, astorage battery for photovoltaic power generation, or the like.

[4-2] Secondary Battery of Second Embodiment

Next, a secondary battery according to a second embodiment will bedescribed.

FIG. 2 is a schematic perspective view schematically showing aconfiguration of a lithium-ion battery as the secondary battery of thesecond embodiment, and FIG. 3 is a schematic cross-sectional viewschematically showing a structure of the lithium-ion battery as thesecondary battery of the second embodiment.

Hereinafter, the secondary battery according to the second embodimentwill be described with reference to these drawings, but different pointsfrom the above-mentioned embodiment will be mainly described, and thedescription of the same matter will be omitted.

As shown in FIG. 2, a lithium-ion battery 100 as the secondary batteryof this embodiment includes a positive electrode composite material 210that functions as a positive electrode, and an electrolyte layer 220 anda negative electrode 30, which are sequentially stacked on the positiveelectrode composite material 210. The lithium-ion battery furtherincludes a current collector 41 in contact with the positive electrodecomposite material 210 at an opposite face side of the positiveelectrode composite material 210 from a face thereof facing theelectrolyte layer 220, and includes a current collector 42 in contactwith the negative electrode 30 at an opposite face side of the negativeelectrode 30 from a face thereof facing the electrolyte layer 220.

Hereinafter, the positive electrode composite material 210 and theelectrolyte layer 220 which are different from the configuration of thelithium-ion battery 100 according to the above-mentioned embodiment willbe described.

[4-2-1] Positive Electrode Composite Material

As shown in FIG. 3, the positive electrode composite material 210 in thelithium-ion battery 100 of this embodiment includes a positive electrodeactive material 211 in a particulate shape and a solid electrolyte 212.In such a positive electrode composite material 210, the batteryreaction rate in the lithium-ion battery 100 can be further increased byincreasing an interfacial area where the positive electrode activematerial 211 in a particulate shape and the solid electrolyte 212 are incontact with each other.

The average particle diameter of the positive electrode active material211 is not particularly limited, but is preferably 0.1 μm or more and150 μm or less, and more preferably 0.3 μm or more and 60 μm or less.

According to this, it becomes easy to achieve both an actual capacitydensity close to the theoretical capacity of the positive electrodeactive material 211 and a high charge-discharge rate.

Note that in this specification, the average particle diameter refers toa volume-based average particle diameter, and can be determined by, forexample, subjecting a dispersion liquid prepared by adding a sample tomethanol and dispersing the sample for 3 minutes using an ultrasonicdisperser to measurement with a particle size distribution analyzeraccording to the Coulter counter method (model TA-II, manufactured byCoulter Electronics, Inc.) using an aperture of 50 μm.

The particle size distribution of the positive electrode active material211 is not particularly limited, and for example, in the particle sizedistribution having one peak, the half width of the peak can be set to0.15 μm or more and 19 μm or less. Further, the particle sizedistribution of the positive electrode active material 211 may have twoor more peaks.

In FIG. 3, the shape of the positive electrode active material 211 in aparticulate shape is shown as a spherical shape, however, the shape ofthe positive electrode active material 211 is not limited to thespherical shape, and it can have various shapes, for example, a columnarshape, a plate shape, a scaly shape, a hollow shape, an indefiniteshape, and the like, and further, two or more types among these may bemixed.

Examples of the positive electrode active material 211 include the samematerials as exemplified as the constituent material of the positiveelectrode 10 in the above-mentioned first embodiment.

In the positive electrode active material 211, for example, a coatinglayer may be formed at a surface for the purpose of reducing theinterface resistance between the positive electrode active material 211and the solid electrolyte 212, or improving an electron conductionproperty, or the like. For example, by forming a thin film of LiNbO₃,Al₂O₃, ZrO₂, Ta₂O₅, or the like at a surface of a particle of thepositive electrode active material 211 composed of LiCoO₂, the interfaceresistance of lithium ion conduction can be further reduced. Thethickness of the coating layer is not particularly limited, but ispreferably 3 nm or more and 1 μm or less.

In this embodiment, the positive electrode composite material 210includes the solid electrolyte 212 in addition to the positive electrodeactive material 211 described above. The solid electrolyte 212 ispresent so as to fill up a gap between particles of the positiveelectrode active material 211 or so as to be in contact with,particularly in close contact with the surface of the positive electrodeactive material 211.

The solid electrolyte 212 is constituted by a material including thesolid electrolyte according to the present disclosure described above.

According to this, the ion conductivity of the solid electrolyte 212becomes particularly excellent. Further, the adhesion of the solidelectrolyte 212 to the positive electrode active material 211 or theelectrolyte layer 220 becomes excellent. Accordingly, the properties andreliability of the lithium-ion battery 100 as a whole can be madeparticularly excellent.

When the content of the positive electrode active material 211 in thepositive electrode composite material 210 is represented by XA [mass %]and the content of the solid electrolyte 212 in the positive electrodecomposite material 210 is represented by XS [mass %], it is preferred tosatisfy a relationship: 0.1≤XS/XA≤8.3, it is more preferred to satisfy arelationship: 0.3≤XS/XA≤2.8, and it is further more preferred to satisfya relationship: 0.6≤XS/XA≤1.4.

Further, the positive electrode composite material 210 may include anelectric conduction assistant, a binder, or the like other than thepositive electrode active material 211 and the solid electrolyte 212.

However, the content of the component other than the positive electrodeactive material 211 and the solid electrolyte 212 in the positiveelectrode composite material 210 is preferably 10 mass % or less, morepreferably 7 mass % or less, and further more preferably 5 mass % orless.

As the electric conduction assistant, any material may be used as longas it is an electric conductor whose electrochemical interaction can beignored at a positive electrode reaction potential, and morespecifically, for example, a carbon material such as acetylene black,Ketjen black, or a carbon nanotube, a noble metal such as palladium orplatinum, an electric conductive oxide such as SnO₂, ZnO, RuO₂, ReO₃, orIr₂O₃, or the like can be used.

The thickness of the positive electrode composite material 210 is notparticularly limited, but is preferably 0.1 μm or more and 500 μm orless, and more preferably 0.3 μm or more and 100 μm or less.

[4-2-2] Electrolyte Layer

The electrolyte layer 220 is preferably constituted by the same materialor the same type of material as the solid electrolyte 212 from theviewpoint of an interfacial impedance between the electrolyte layer 220and the positive electrode composite material 210, but may beconstituted by a material different from the solid electrolyte 212. Forexample, the electrolyte layer 220 contains the solid electrolyteaccording to the present disclosure described above, but may beconstituted by a material having a different formulation from the solidelectrolyte 212. Further, the electrolyte layer 220 may be a crystallinematerial or an amorphous material of another oxide solid electrolytewhich is not the solid electrolyte according to the present disclosure,a sulfide solid electrolyte, a nitride solid electrolyte, a halide solidelectrolyte, a hydride solid electrolyte, a dry polymer electrolyte, ora quasi-solid electrolyte, or may be constituted by a material in whichtwo or more types selected from these are combined.

When the electrolyte layer 220 is constituted by a material containingthe solid electrolyte according to the present disclosure, the contentof the solid electrolyte according to the present disclosure in theelectrolyte layer 220 is preferably 80 mass % or more, more preferably90 mass % or more, and further more preferably 95 mass % or more.

According to this, the effect of the present disclosure as describedabove is more remarkably exhibited.

Examples of a crystalline oxide include Li_(0.35)La_(0.55)TiO₃,Li_(0.2)La_(0.27)NbO₃, and a perovskite-type crystal or aperovskite-like crystal in which the elements constituting a crystalthereof are partially substituted with N, F, Al, Sr, Sc, Nb, Ta, Sb, alanthanoid element, or the like, Li₇La₃Zr₂O₁₂, Li₅La₃Nb₂O₁₂,Li₅BaLa₂TaO₁₂, and a garnet-type crystal or a garnet-like crystal inwhich the elements constituting a crystal thereof are partiallysubstituted with N, F, Al, Sr, Sc, Nb, Ta, Sb, a lanthanoid element, orthe like, Li_(1.3)Ti_(1.7)Al_(0.3)(PO₄)₃,Li_(1.4)Al_(0.4)Ti_(1.6)(PO₄)₃, Li_(1.4)Al_(0.4)Ti_(1.4)Ge_(0.2)(PO₄)₃,and a NASICON-type crystal in which the elements constituting a crystalthereof are partially substituted with N, F, Al, Sr, Sc, Nb, Ta, Sb, alanthanoid element, or the like, a LISICON-type crystal such asLi₁₄ZnGe₄O₁₆, and other crystalline materials such asLi_(3.4)V_(0.6)Si_(0.4)O₄, Li_(3.6)V_(0.4)Ge_(0.6)O₄, andLi_(2+x)C_(1-x)B_(x)O₃.

Examples of a crystalline sulfide include Li₁₀GeP₂S₁₂, Li_(9.6)P₃S₁₂,Li_(9.54)Si_(1.74)P_(1.44)S_(11.7)Cl_(0.3), and Li₃PS₄.

Examples of other amorphous materials include Li₂O—TiO₂,La₂O₃—Li₂O—TiO₂, LiNbO₃, LiSO₄, Li₄SiO₄, Li₃PO₄—Li₄SiO₄, Li₄GeO₄—Li₃VO₄,Li₄SiO₄—Li₃VO₄, Li₄GeO₄—Zn₂GeO₂, Li₄SiO₄—LiMoO₄, Li₄SiO₄—Li₄ZrO₄,SiO₂—P₂O₅—Li₂O, SiO₂—P₂O₅—LiCl, Li₂O—LiCl—B₂O₃, LiAlCl₄, LiAlF₄,LiF—Al₂O₃, LiBr—Al₂O₃, Li_(2.88)PO_(3.73)N_(0.14), Li₃N—LiCl, Li₆NBr₃,Li₂S—SiS₂, and Li₂S—SiS₂—P₂S₅.

When the electrolyte layer 220 is constituted by a crystalline material,the crystalline material preferably has a crystal structure such as acubic crystal having small crystal plane anisotropy in the direction oflithium ion conduction. Further, when the electrolyte layer 220 isconstituted by an amorphous material, the anisotropy in lithium ionconduction becomes small. Therefore, the crystalline material and theamorphous material as described above are both preferred as a solidelectrolyte constituting the electrolyte layer 220.

The thickness of the electrolyte layer 220 is preferably 0.1 μm or moreand 100 μm or less, and more preferably 0.2 μm or more and 10 μm orless. When the thickness of the electrolyte layer 220 is a value withinthe above range, the internal resistance of the electrolyte layer 220can be further decreased, and also the occurrence of a short circuitbetween the positive electrode composite material 210 and the negativeelectrode 30 can be more effectively prevented.

For the purpose of improving the adhesion between the electrolyte layer220 and the negative electrode 30, or improving the output or batterycapacity of the lithium-ion battery 100 by an increase in specificsurface area, or the like, for example, a three-dimensional patternstructure such as a dimple, trench, or pillar pattern may be formed at asurface of the electrolyte layer 220 to come in contact with thenegative electrode 30.

[4-3] Secondary Battery of Third Embodiment

Next, a secondary battery according to a third embodiment will bedescribed.

FIG. 4 is a schematic perspective view schematically showing aconfiguration of a lithium-ion battery as the secondary battery of thethird embodiment, and FIG. 5 is a schematic cross-sectional viewschematically showing a structure of the lithium-ion battery as thesecondary battery of the third embodiment.

Hereinafter, the secondary battery according to the third embodimentwill be described with reference to these drawings, but different pointsfrom the above-mentioned embodiments will be mainly described, and thedescription of the same matter will be omitted.

As shown in FIG. 4, a lithium-ion battery 100 as the secondary batteryof this embodiment includes a positive electrode 10, and an electrolytelayer 220 and a negative electrode composite material 330 that functionsas a negative electrode, which are sequentially stacked on the positiveelectrode 10. The lithium-ion battery further includes a currentcollector 41 in contact with the positive electrode 10 at an oppositeface side of the positive electrode 10 from a face thereof facing theelectrolyte layer 220, and includes a current collector 42 in contactwith the negative electrode composite material 330 at an opposite faceside of the negative electrode composite material 330 from a facethereof facing the electrolyte layer 220.

Hereinafter, the negative electrode composite material 330 which isdifferent from the configuration of the lithium-ion battery 100according to the above-mentioned embodiments will be described.

[4-3-1] Negative Electrode Composite Material

As shown in FIG. 5, the negative electrode composite material 330 in thelithium-ion battery 100 of this embodiment includes a negative electrodeactive material 331 in a particulate shape and a solid electrolyte 212.In such a negative electrode composite material 330, the batteryreaction rate in the lithium-ion battery 100 can be further increased byincreasing an interfacial area where the negative electrode activematerial 331 in a particulate shape and the solid electrolyte 212 are incontact with each other.

The average particle diameter of the negative electrode active material331 is not particularly limited, but is preferably 0.1 μm or more and150 μm or less, and more preferably 0.3 μm or more and 60 μm or less.

According to this, it becomes easy to achieve both an actual capacitydensity close to the theoretical capacity of the negative electrodeactive material 331 and a high charge-discharge rate.

The particle size distribution of the negative electrode active material331 is not particularly limited, and for example, in the particle sizedistribution having one peak, the half width of the peak can be set to0.1 μm or more and 18 μm or less. Further, the particle sizedistribution of the negative electrode active material 331 may have twoor more peaks.

In FIG. 5, the shape of the negative electrode active material 331 in aparticulate shape is shown as a spherical shape, however, the shape ofthe negative electrode active material 331 is not limited to thespherical shape, and it can have various shapes, for example, a columnarshape, a plate shape, a scaly shape, a hollow shape, an indefiniteshape, and the like, and further, two or more types among these may bemixed.

Examples of the negative electrode active material 331 include the samematerials as exemplified as the constituent material of the negativeelectrode 30 in the above-mentioned first embodiment.

In this embodiment, the negative electrode composite material 330includes the solid electrolyte 212 in addition to the negative electrodeactive material 331 described above. The solid electrolyte 212 ispresent so as to fill up a gap between particles of the negativeelectrode active material 331 or so as to be in contact with,particularly in close contact with the surface of the negative electrodeactive material 331.

The solid electrolyte 212 is constituted by a material including thesolid electrolyte according to the present disclosure described above.

According to this, the ion conductivity of the solid electrolyte 212becomes particularly excellent. Further, the adhesion of the solidelectrolyte 212 to the negative electrode active material 331 or theelectrolyte layer 220 can be made excellent. Accordingly, the propertiesand reliability of the lithium-ion battery 100 as a whole can be madeparticularly excellent.

When the content of the negative electrode active material 331 in thenegative electrode composite material 330 is represented by XB [mass %]and the content of the solid electrolyte 212 in the negative electrodecomposite material 330 is represented by XS [mass %], it is preferred tosatisfy a relationship: 0.14≤XS/XB≤26, it is more preferred to satisfy arelationship: 0.44≤XS/XB≤4.1, and it is further more preferred tosatisfy a relationship: 0.89≤XS/XB≤2.1.

Further, the negative electrode composite material 330 may include anelectric conduction assistant, a binder, or the like other than thenegative electrode active material 331 and the solid electrolyte 212.

However, the content of the component other than the negative electrodeactive material 331 and the solid electrolyte 212 in the negativeelectrode composite material 330 is preferably 10 mass % or less, morepreferably 7 mass % or less, and further more preferably 5 mass % orless.

As the electric conduction assistant, any material may be used as longas it is an electric conductor whose electrochemical interaction can beignored at a negative electrode reaction potential, and morespecifically, for example, a carbon material such as acetylene black,Ketjen black, or a carbon nanotube, a noble metal such as palladium orplatinum, an electric conductive oxide such as SnO₂, ZnO, RuO₂, ReO₃, orIr₂O₃, or the like can be used.

The thickness of the negative electrode composite material 330 is notparticularly limited, but is preferably 0.1 μm or more and 500 μm orless, and more preferably 0.3 m or more and 100 μm or less.

[4-4] Secondary Battery of Fourth Embodiment

Next, a secondary battery according to a fourth embodiment will bedescribed.

FIG. 6 is a schematic perspective view schematically showing aconfiguration of a lithium-ion battery as the secondary battery of thefourth embodiment, and FIG. 7 is a schematic cross-sectional viewschematically showing a structure of the lithium-ion battery as thesecondary battery of the fourth embodiment.

Hereinafter, the secondary battery according to the fourth embodimentwill be described with reference to these drawings, but different pointsfrom the above-mentioned embodiments will be mainly described, and thedescription of the same matter will be omitted.

As shown in FIG. 6, a lithium-ion battery 100 as the secondary batteryof this embodiment includes a positive electrode composite material 210,and a solid electrolyte layer 20 and a negative electrode compositematerial 330, which are sequentially stacked on the positive electrodecomposite material 210. The lithium-ion battery further includes acurrent collector 41 in contact with the positive electrode compositematerial 210 at an opposite face side of the positive electrodecomposite material 210 from a face thereof facing the solid electrolytelayer 20, and includes a current collector 42 in contact with thenegative electrode composite material 330 at an opposite face side ofthe negative electrode composite material 330 from a face thereof facingthe solid electrolyte layer 20.

It is preferred that the respective portions satisfy the same conditionsas described for the respective portions corresponding thereto in theabove-mentioned embodiments.

In the first to fourth embodiments, another layer may be providedbetween layers or at a surface of a layer of the respective layersconstituting the lithium-ion battery 100. Examples of such a layerinclude an adhesive layer, an insulating layer, and a protective layer.

[5] Method for Producing Secondary Battery

Next, a method for producing the above-mentioned secondary battery willbe described.

[5-1] Method for Producing Secondary Battery of First Embodiment

Hereinafter, a method for producing the secondary battery according tothe first embodiment will be described.

FIG. 8 is a flowchart showing the method for producing the lithium-ionbattery as the secondary battery of the first embodiment, FIGS. 9 and 10are schematic views schematically showing the method for producing thelithium-ion battery as the secondary battery of the first embodiment,and FIG. 11 is a schematic cross-sectional view schematically showinganother method for forming a solid electrolyte layer.

As shown in FIG. 8, the method for producing the lithium-ion battery 100of this embodiment includes Step S1, Step S2, Step S3, and Step S4.

Step S1 is a step of forming the solid electrolyte layer 20. Step S2 isa step of forming the positive electrode 10. Step S3 is a step offorming the negative electrode 30. Step S4 is a step of forming thecurrent collectors 41 and 42.

[5-1-1] Step S1

In the step of forming the solid electrolyte layer 20 of Step S1, thesolid electrolyte layer 20 is formed by, for example, a green sheetmethod using the calcined body according to the present disclosure asdescribed above, that is, a calcined body containing a precursor oxideand an oxoacid compound. More specifically, the solid electrolyte layer20 can be formed as follows.

That is, first, for example, a solution in which a binder such aspolypropylene carbonate is dissolved in a solvent such as 1,4-dioxane isprepared, and the solution and the calcined body according to thepresent disclosure are mixed, whereby a slurry 20 m is obtained. In thepreparation of the slurry 20 m, a dispersant, a diluent, a humectant, orthe like may be further used as needed.

Subsequently, by using the slurry 20 m, a solid electrolyte formingsheet 20 s is formed. More specifically, as shown in FIG. 9, forexample, by using a fully automatic film applicator 500, the slurry 20 mis applied to a predetermined thickness onto a base material 506 such asa polyethylene terephthalate film, whereby the solid electrolyte formingsheet 20 s is formed. The fully automatic film applicator 500 includesan application roller 501 and a doctor roller 502. A squeegee 503 isprovided so as to come in contact with the doctor roller 502 from above.A conveyance roller 504 is provided below the application roller 501 ata position opposite thereto, and a stage 505 on which the base material506 is placed is conveyed in a fixed direction by inserting the stage505 between the application roller 501 and the conveyance roller 504.The slurry 20 m is fed to a side where the squeegee 503 is providedbetween the application roller 501 and the doctor roller 502 disposedwith a gap therebetween in the conveyance direction of the stage 505.The slurry 20 m with a predetermined thickness is applied to the surfaceof the application roller 501 by rotating the application roller 501 andthe doctor roller 502 so as to extrude the slurry 20 m downward from thegap. Then, along with this, by rotating the conveyance roller 504, thestage 505 is conveyed so that the base material 506 comes in contactwith the application roller 501 to which the slurry 20 m has beenapplied. By doing this, the slurry 20 m applied to the applicationroller 501 is transferred in a sheet form to the base material 506,whereby the solid electrolyte forming sheet 20 s is formed.

Thereafter, the solvent is removed from the solid electrolyte formingsheet 20 s formed on the base material 506, and the solid electrolyteforming sheet 20 s is detached from the base material 506 and punched toa predetermined size using a punching die as shown in FIG. 10, whereby amolded material 20 f is formed.

Thereafter, the molded material 20 f is subjected to a heating step at atemperature of 700° C. or higher and 1000° C. or lower, whereby thesolid electrolyte layer 20 as a main fired body is obtained. The heatingtime and atmosphere in the heating step are as described above.

The solid electrolyte forming sheet 20 s with a predetermined thicknessmay be formed by pressing and extruding the slurry 20 m by theapplication roller 501 and the doctor roller 502 so that the sintereddensity of the solid electrolyte layer 20 after firing becomes 90% ormore.

[5-1-2] Step S2

After Step S1, the process proceeds to Step S2.

In the step of forming the positive electrode 10 of Step S2, thepositive electrode 10 is formed at one face of the solid electrolytelayer 20. More specifically, for example, first, by using a sputteringdevice, sputtering is performed using LiCoO₂ as a target in an inert gassuch as argon gas, whereby a LiCoO₂ layer is formed at a surface of thesolid electrolyte layer 20. Thereafter, the LiCoO₂ layer formed on thesolid electrolyte layer 20 is fired in an oxidizing atmosphere so as toconvert the crystal of the LiCoO₂ layer into a high-temperature phasecrystal, whereby the LiCoO₂ layer can be converted into the positiveelectrode 10. The firing conditions for the LiCoO₂ layer are notparticularly limited, but the heating temperature can be set to 400° C.or higher and 600° C. or lower, and the heating time can be set to 1hour or more and 3 hours or less.

[5-1-3] Step S3

After Step S2, the process proceeds to Step S3.

In the step of forming the negative electrode 30 of Step S3, thenegative electrode 30 is formed at the other face of the solidelectrolyte layer 20, that is, a face at an opposite side from the faceat which the positive electrode 10 is formed. More specifically, forexample, by using a vacuum deposition device or the like, the negativeelectrode 30 can be formed by forming a thin film of metal Li at a faceof the solid electrolyte layer 20 at an opposite side from the face atwhich the positive electrode 10 is formed. The thickness of the negativeelectrode 30 can be set to, for example, 0.1 μm or more and 500 μm orless.

[5-1-4] Step S4

After Step S3, the process proceeds to Step S4.

In the step of forming the current collectors 41 and 42 of Step S4, thecurrent collector 41 is formed so as to come in contact with thepositive electrode 10, and the current collector 42 is formed so as tocome in contact with the negative electrode 30. More specifically, forexample, an aluminum foil formed into a circular shape by punching orthe like is joined to the positive electrode 10 by pressing, whereby thecurrent collector 41 can be formed. Further, for example, a copper foilformed into a circular shape by punching or the like is joined to thenegative electrode 30 by pressing, whereby the current collector 42 canbe formed. The thickness of each of the current collectors 41 and 42 isnot particularly limited, but can be set to, for example, 10 μm or moreand 60 μm or less. In this step, only one of the current collectors 41and 42 may be formed.

The method for forming the solid electrolyte layer 20 is not limited tothe green sheet method shown in Step S1. As another method for formingthe solid electrolyte layer 20, for example, a method as described belowcan be adopted. That is, as shown in FIG. 11, the molded material 20 fmay be obtained by filling the calcined body according to the presentdisclosure in a powder form, that is, a calcined body containing aprecursor oxide and an oxoacid compound in a pellet die 80, closing thepellet die using a lid 81, and pressing the lid 81 to perform uniaxialpress molding. A treatment for the molded material 20 f thereafter canbe performed in the same manner as described above. As the pellet die80, a die including an exhaust port (not shown) can be favorably used.

[5-2] Method for Producing Secondary Battery of Second Embodiment

Next, a method for producing the secondary battery according to thesecond embodiment will be described.

FIG. 12 is a flowchart showing the method for producing the lithium-ionbattery as the secondary battery of the second embodiment, and FIGS. 13and 14 are schematic views schematically showing the method forproducing the lithium-ion battery as the secondary battery of the secondembodiment.

Hereinafter, the method for producing the secondary battery according tothe second embodiment will be described with reference to thesedrawings, but different points from the above-mentioned embodiment willbe mainly described, and the description of the same matter will beomitted.

As shown in FIG. 12, the method for producing the lithium-ion battery100 of this embodiment includes Step S11, Step S12, Step S13, and StepS14.

Step S11 is a step of forming the positive electrode composite material210. Step S12 is a step of forming the electrolyte layer 220. Step S13is a step of forming the negative electrode 30. Step S14 is a step offorming the current collectors 41 and 42.

[5-2-1] Step S11

In the step of forming the positive electrode composite material 210 ofStep S11, the positive electrode composite material 210 is formed.

The positive electrode composite material 210 can be formed, forexample, as follows.

That is, first, for example, a slurry 210 m as a mixture of the positiveelectrode active material 211 such as LiCoO₂, the calcined bodyaccording to the present disclosure as described above, that is, acalcined body containing a precursor oxide and an oxoacid compound, abinder such as polypropylene carbonate, and a solvent such as1,4-dioxane is obtained. In the preparation of the slurry 210 m, adispersant, a diluent, a humectant, or the like may be further used asneeded.

Subsequently, by using the slurry 210 m, a positive electrode compositematerial forming sheet 210 s is formed. More specifically, as shown inFIG. 13, for example, by using a fully automatic film applicator 500,the slurry 210 m is applied to a predetermined thickness onto a basematerial 506 such as a polyethylene terephthalate film, whereby thepositive electrode composite material forming sheet 210 s is formed.

Thereafter, the solvent is removed from the positive electrode compositematerial forming sheet 210 s formed on the base material 506, and thepositive electrode composite material forming sheet 210 s is detachedfrom the base material 506 and punched to a predetermined size using apunching die as shown in FIG. 14, whereby a molded material 210 f isformed.

Thereafter, the molded material 210 f is subjected to a heating step ata temperature of 700° C. or higher and 1000° C. or lower, whereby thepositive electrode composite material 210 including a solid electrolyteis obtained. The heating time and atmosphere in the heating step are asdescribed above.

[5-2-2] Step S12

After Step S11, the process proceeds to Step S12.

In the step of forming the electrolyte layer 220 of Step S12, theelectrolyte layer 220 is formed at one face 210 b of the positiveelectrode composite material 210. More specifically, for example, byusing a sputtering device, sputtering is performed using LiCoO₂ as atarget in an inert gas such as argon gas, whereby a LiCoO₂ layer isformed at a surface of the positive electrode composite material 210.Thereafter, the LiCoO₂ layer formed on the positive electrode compositematerial 210 is fired in an oxidizing atmosphere so as to convert thecrystal of the LiCoO₂ layer into a high-temperature phase crystal,whereby the LiCoO₂ layer can be converted into the electrolyte layer220. The firing conditions for the LiCoO₂ layer are not particularlylimited, but the heating temperature can be set to 400° C. or higher and600° C. or lower, and the heating time can be set to 1 hour or more and3 hours or less.

[5-2-3] Step S13

After Step S12, the process proceeds to Step S13.

In the step of forming the negative electrode 30 of Step S13, thenegative electrode 30 is formed at an opposite face side of theelectrolyte layer 220 from a face thereof facing the positive electrodecomposite material 210. More specifically, for example, by using avacuum deposition device or the like, the negative electrode 30 can beformed by forming a thin film of metal Li at an opposite face side ofthe electrolyte layer 220 from a face thereof facing the positiveelectrode composite material 210.

[5-2-4] Step S14

After Step S13, the process proceeds to Step S14.

In the step of forming the current collectors 41 and 42 of Step S14, thecurrent collector 41 is formed so as to come in contact with the otherface of the positive electrode composite material 210, that is, a face210 a at an opposite side from the face 210 b at which the electrolytelayer 220 is formed, and the current collector 42 is formed so as tocome in contact with the negative electrode 30.

The methods for forming the positive electrode composite material 210and the electrolyte layer 220 are not limited to the above-mentionedmethods. For example, the positive electrode composite material 210 andthe electrolyte layer 220 may be formed as follows. That is, first, aslurry as a mixture of the calcined body according to the presentdisclosure, that is, a calcined body containing a precursor oxide and anoxoacid compound, a binder, and a solvent is obtained. Then, theobtained slurry is fed to a fully automatic film applicator 500 andapplied onto the base material 506, whereby an electrolyte forming sheetis formed. Thereafter, the electrolyte forming sheet and the positiveelectrode composite material forming sheet 210 s formed in the samemanner as described above are pressed in a stacked state and bonded toeach other. Thereafter, a stacked sheet obtained by bonding the sheetsto each other is punched to form a molded material, and the moldedmaterial is fired in an oxidizing atmosphere, whereby a stacked body ofthe positive electrode composite material 210 and the electrolyte layer220 may be obtained.

[5-3] Method for Producing Secondary Battery of Third Embodiment

Next, a method for producing the secondary battery according to thethird embodiment will be described.

FIG. 15 is a flowchart showing the method for producing the lithium-ionbattery as the secondary battery of the third embodiment, and FIGS. 16and 17 are schematic views schematically showing the method forproducing the lithium-ion battery as the secondary battery of the thirdembodiment.

Hereinafter, the method for producing the secondary battery according tothe third embodiment will be described with reference to these drawings,but different points from the above-mentioned embodiments will be mainlydescribed, and the description of the same matter will be omitted.

As shown in FIG. 15, the method for producing the lithium-ion battery100 of this embodiment includes Step S21, Step S22, Step S23, and StepS24.

Step S21 is a step of forming the negative electrode composite material330. Step S22 is a step of forming the electrolyte layer 220. Step S23is a step of forming the positive electrode 10. Step S24 is a step offorming the current collectors 41 and 42.

[5-3-1] Step S21

In the step of forming the negative electrode composite material 330 ofStep S21, the negative electrode composite material 330 is formed.

The negative electrode composite material 330 can be formed, forexample, as follows.

That is, first, for example, a slurry 330 m as a mixture of the negativeelectrode active material 331 such as Li₄TisO₁₂, the calcined bodyaccording to the present disclosure, that is, a calcined body containinga precursor oxide and an oxoacid compound, a binder such aspolypropylene carbonate, and a solvent such as 1,4-dioxane is obtained.In the preparation of the slurry 330 m, a dispersant, a diluent, ahumectant, or the like may be further used as needed.

Subsequently, by using the slurry 330 m, a negative electrode compositematerial forming sheet 330 s is formed. More specifically, as shown inFIG. 16, for example, by using a fully automatic film applicator 500,the slurry 330 m is applied to a predetermined thickness onto a basematerial 506 such as a polyethylene terephthalate film, whereby thenegative electrode composite material forming sheet 330 s is formed.

Thereafter, the solvent is removed from the negative electrode compositematerial forming sheet 330 s formed on the base material 506, and thenegative electrode composite material forming sheet 330 s is detachedfrom the base material 506 and punched to a predetermined size using apunching die as shown in FIG. 17, whereby a molded material 330 f isformed.

Thereafter, the molded material 330 f is subjected to a heating step ata temperature of 700° C. or higher and 1000° C. or lower, whereby thenegative electrode composite material 330 including a solid electrolyteis obtained. The heating time and atmosphere in the heating step are asdescribed above.

[5-3-2] Step S22

After Step S21, the process proceeds to Step S22.

In the step of forming the electrolyte layer 220 of Step S22, theelectrolyte layer 220 is formed at one face 330 a of the negativeelectrode composite material 330. More specifically, for example, byusing a sputtering device, sputtering is performed usingLi_(2.2)C_(0.8)B_(0.2)O₃ which is a solid solution of Li₂CO₃ and Li₃BO₃as a target in an inert gas such as argon gas, whereby aLi_(2.2)C_(0.8)B_(0.2)O₃ layer is formed at a surface of the negativeelectrode composite material 330. Thereafter, theLi_(2.2)C_(0.8)B_(0.2)O₃ layer formed on the negative electrodecomposite material 330 is fired in an oxidizing atmosphere so as toconvert the crystal of the Li_(2.2)C_(0.8)B_(0.2)O₃ layer into ahigh-temperature phase crystal, whereby the Li_(2.2)C_(0.8)B_(0.2)O₃layer can be converted into the electrolyte layer 220. The firingconditions for the Li_(2.2)C_(0.8)B_(0.2)O₃ layer are not particularlylimited, but the heating temperature can be set to 400° C. or higher and600° C. or lower, and the heating time can be set to 1 hour or more and3 hours or less.

[5-3-3] Step S23

After Step S22, the process proceeds to Step S23.

In the step of forming the positive electrode 10 of Step S23, thepositive electrode 10 is formed at one face 220 a side of theelectrolyte layer 220, that is, an opposite face side of the electrolytelayer 220 from a face thereof facing the negative electrode compositematerial 330. More specifically, for example, first, by using a vacuumdeposition device or the like, a LiCoO₂ layer is formed at one face 220a of the electrolyte layer 220. Thereafter, a stacked body of theelectrolyte layer 220 at which the LiCoO₂ layer is formed, and thenegative electrode composite material 330 is fired so as to convert thecrystal of the LiCoO₂ layer into a high-temperature phase crystal,whereby the LiCoO₂ layer can be converted into the positive electrode10. The firing conditions for the LiCoO₂ layer are not particularlylimited, but the heating temperature can be set to 400° C. or higher and600° C. or lower, and the heating time can be set to 1 hour or more and3 hours or less.

[5-3-4] Step S24

After Step S23, the process proceeds to Step S24.

In the step of forming the current collectors 41 and 42 of Step S24, thecurrent collector 41 is formed so as to come in contact with one face 10a of the positive electrode 10, that is, the face 10 a of the positiveelectrode 10 at an opposite side from the face at which the electrolytelayer 220 is formed, and the current collector 42 is formed so as tocome in contact with the other face of the negative electrode compositematerial 330, that is, a face 330 b of the negative electrode compositematerial 330 at an opposite side from the face 330 a at which theelectrolyte layer 220 is formed.

The methods for forming the negative electrode composite material 330and the electrolyte layer 220 are not limited to the above-mentionedmethods. For example, the negative electrode composite material 330 andthe electrolyte layer 220 may be formed as follows. That is, first, aslurry as a mixture of the calcined body according to the presentdisclosure, that is, a calcined body containing a precursor oxide and anoxoacid compound, a binder, and a solvent is obtained. Then, theobtained slurry is fed to a fully automatic film applicator 500 andapplied onto the base material 506, whereby an electrolyte forming sheetis formed. Thereafter, the electrolyte forming sheet and the negativeelectrode composite material forming sheet 330 s formed in the samemanner as described above are pressed in a stacked state and bonded toeach other. Thereafter, a stacked sheet obtained by bonding the sheetsto each other is punched to form a molded material, and the moldedmaterial is fired in an oxidizing atmosphere, whereby a stacked body ofthe negative electrode composite material 330 and the electrolyte layer220 may be obtained.

[5-4] Method for Producing Secondary Battery of Fourth Embodiment

Next, a method for producing the secondary battery according to thefourth embodiment will be described.

FIG. 18 is a flowchart showing the method for producing the lithium-ionbattery as the secondary battery of the fourth embodiment, and FIG. 19is a schematic view schematically showing the method for producing thelithium-ion battery as the secondary battery of the fourth embodiment.

Hereinafter, the method for producing the secondary battery according tothe fourth embodiment will be described with reference to thesedrawings, but different points from the above-mentioned embodiments willbe mainly described, and the description of the same matter will beomitted.

As shown in FIG. 18, the method for producing the lithium-ion battery100 of this embodiment includes Step S31, Step S32, Step S33, Step S34,Step S35, and Step S36.

Step S31 is a step of forming a sheet for forming the positive electrodecomposite material 210. Step S32 is a step of forming a sheet forforming the negative electrode composite material 330. Step S33 is astep of forming a sheet for forming the solid electrolyte layer 20. StepS34 is a step of forming a molded material 450 f of molding a stackedbody of the sheet for forming the positive electrode composite material210, the sheet for forming the negative electrode composite material330, and the sheet for forming the solid electrolyte layer 20 into apredetermined shape. Step S35 is a step of firing the molded material450 f. Step S36 is a step of forming the current collectors 41 and 42.

In the following description, a description will be made by assumingthat Step S32 is performed after Step S31, and Step S33 is performedafter Step S32, however, the order of Step S31, Step S32, and Step S33is not limited thereto, and the order of the steps may be changed, orthe steps may be concurrently performed.

[5-4-1] Step S31

In the step of forming a sheet for forming the positive electrodecomposite material 210 of Step S31, a positive electrode compositematerial forming sheet 210 s that is the sheet for forming the positiveelectrode composite material 210 is formed.

The positive electrode composite material forming sheet 210 s can beformed, for example, in the same manner as described in the above secondembodiment.

The positive electrode composite material forming sheet 210 s obtainedin this step is preferably one obtained by removing the solvent from theslurry 210 m used for forming the positive electrode composite materialforming sheet 210 s.

[5-4-2] Step S32

After Step S31, the process proceeds to Step S32.

In the step of forming a sheet for forming the negative electrodecomposite material 330 of Step S32, a negative electrode compositematerial forming sheet 330 s that is the sheet for forming the negativeelectrode composite material 330 is formed.

The negative electrode composite material forming sheet 330 s can beformed, for example, in the same manner as described in the above thirdembodiment.

The negative electrode composite material forming sheet 330 s obtainedin this step is preferably one obtained by removing the solvent from theslurry 330 m used for forming the negative electrode composite materialforming sheet 330 s.

[5-4-3] Step S33

After Step S32, the process proceeds to Step S33.

In the step of forming a sheet for forming the solid electrolyte layer20 of Step S33, a solid electrolyte forming sheet 20 s that is the sheetfor forming the solid electrolyte layer 20 is formed.

The solid electrolyte forming sheet 20 s can be formed, for example, inthe same manner as described in the above first embodiment.

The solid electrolyte forming sheet 20 s obtained in this step ispreferably one obtained by removing the solvent from the slurry 20 mused for forming the solid electrolyte forming sheet 20 s.

[5-4-4] Step S34

After Step S33, the process proceeds to Step S34.

In the step of forming the molded material 450 f of Step S34, thepositive electrode composite material forming sheet 210 s, the solidelectrolyte forming sheet 20 s, and the negative electrode compositematerial forming sheet 330 s are pressed in a state of being stacked inthis order and bonded to one another. Thereafter, as shown in FIG. 19, astacked sheet obtained by bonding the sheets to one another is punched,whereby the molded material 450 f is obtained.

[5-4-5] Step S35

After Step S34, the process proceeds to Step S35.

In the step of firing the molded material 450 f of Step S35, the moldedmaterial 450 f is subjected to a heating step at a temperature of 700°C. or higher and 1000° C. or lower. By doing this, a portion constitutedby the positive electrode composite material forming sheet 210 s isconverted into the positive electrode composite material 210, a portionconstituted by the solid electrolyte forming sheet 20 s is convertedinto the solid electrolyte layer 20, and a portion constituted by thenegative electrode composite material forming sheet 330 s is convertedinto the negative electrode composite material 330. That is, a firedbody of the molded material 450 f is a stacked body of the positiveelectrode composite material 210, the solid electrolyte layer 20, andthe negative electrode composite material 330. The heating time andatmosphere in the heating step are as described above.

[5-4-6] Step S36

After Step S35, the process proceeds to Step S36.

In the step of forming the current collectors 41 and 42 of Step S36, thecurrent collector 41 is formed so as to come in contact with the face210 a of the positive electrode composite material 210, and the currentcollector 42 is formed so as to come in contact with the face 330 b ofthe negative electrode composite material 330.

Hereinabove, preferred embodiments of the present disclosure have beendescribed, however, the present disclosure is not limited thereto.

For example, the method for producing a solid electrolyte may furtherinclude another step in addition to the steps as described above.

Further, when the present disclosure is applied to a secondary battery,the configuration of the secondary battery is not limited to those ofthe above-mentioned embodiments.

For example, when the present disclosure is applied to a secondarybattery, the secondary battery is not limited to a lithium-ion battery,and may be, for example, a secondary battery in which a porous separatoris provided between a positive electrode composite material and anegative electrode, and the separator is impregnated with an electrolytesolution.

Further, when the present disclosure is applied to a secondary battery,the production method therefor is not limited to those of theabove-mentioned embodiments. For example, the order of the steps in theproduction of the secondary battery may be made different from that inthe above-mentioned embodiments.

Further, in the above-mentioned embodiments, a description has been madeby assuming that the solid electrolyte according to the presentdisclosure constitutes a part of a secondary battery, particularly apart of an all-solid-state lithium secondary battery that is anall-solid-state secondary battery, however, the solid electrolyteaccording to the present disclosure may constitute, for example, a partother than an all-solid-state secondary battery or may constitute a partother than a secondary battery.

EXAMPLES

Next, specific Examples of the present disclosure will be described.Note that in the following description, room temperature refers to 25°C. at 1 atm. Further, a treatment or measurement for which thetemperature condition is not particularly specified was performed at 25°C., and a treatment or measurement for which the pressure condition isnot particularly specified was performed in a 1 atm environment.

[6] Production of Calcined Body

First, calcined bodies to be used in the production of solidelectrolytes of the below-mentioned respective Examples and respectiveComparative Examples were produced.

In the preparation of the respective calcined bodies, metal compoundsolutions described below were used.

[6-1] Preparation of Metal Compound Solutions Used in Production ofCalcined Bodies

[6-1-1] Preparation of 2-n-Butoxyethanol Solution of Lithium Nitrate

In a 30-g reagent bottle made of Pyrex (Pyrex: trademark of CorningIncorporated, Pyrex is a registered trademark) equipped with a magneticstirring bar, 1.3789 g of lithium nitrate with a purity of 99.95% (3N5,manufactured by Kanto Chemical Co., Inc.) and 18.6211 g of2-n-butoxyethanol (ethylene glycol monobutyl ether) (Cica Special Grade,manufactured by Kanto Chemical Co., Inc.) were weighed. Then, thereagent bottle was placed on a hot plate with a magnetic stirrerfunction, and lithium nitrate was completely dissolved in2-n-butoxyethanol while stirring at 170° C. for 1 hour. The resultingsolution was gradually cooled to room temperature, whereby a2-n-butoxyethanol solution of 1 mol/kg lithium nitrate was obtained.

[6-1-2] Preparation of 2-n-Butoxyethanol Solution of Lanthanum Nitrate

In a 30-g reagent bottle made of Pyrex equipped with a magnetic stirringbar, 8.6608 g of lanthanum nitrate hexahydrate (4N, manufactured byKanto Chemical Co., Inc.) and 11.3392 g of 2-n-butoxyethanol (CicaSpecial Grade, manufactured by Kanto Chemical Co., Inc.) were weighed.Then, the reagent bottle was placed on a hot plate with a magneticstirrer function, and lanthanum nitrate hexahydrate was completelydissolved in 2-n-butoxyethanol while stirring at 140° C. for 30 minutes.The resulting solution was gradually cooled to room temperature, wherebya 2-n-butoxyethanol solution of 1 mol/kg lanthanum nitrate hexahydratewas obtained.

[6-1-3] Preparation of 2-n-Butoxyethanol Solution of ZirconiumTetra-n-Butoxide

In a 20-g reagent bottle made of Pyrex equipped with a magnetic stirringbar, 3.8368 g of zirconium tetra-n-butoxide (manufactured by KojundoChemical Lab. Co., Ltd.) and 6.1632 g of 2-n-butoxyethanol (Cica SpecialGrade, manufactured by Kanto Chemical Co., Inc.) were weighed. Then, thereagent bottle was placed on a hot plate with a magnetic stirrerfunction, and zirconium tetra-n-butoxide was completely dissolved in2-n-butoxyethanol while stirring at room temperature for 30 minutes,whereby a 2-n-butoxyethanol solution of 1 mol/kg zirconiumtetra-n-butoxide was obtained.

[6-1-4] Preparation of 2-n-Butoxyethanol Solution of TungstenPentaethoxide

In a 20-g reagent bottle made of Pyrex equipped with a magnetic stirringbar, 4.0915 g of tungsten pentaethoxide (manufactured by KojundoChemical Lab. Co., Ltd.) and 5.9085 g of 2-n-butoxyethanol (Cica SpecialGrade, manufactured by Kanto Chemical Co., Inc.) were weighed. Then, thereagent bottle was placed on a hot plate with a magnetic stirrerfunction, and tungsten pentaethoxide was completely dissolved in2-n-butoxyethanol while stirring at room temperature for 30 minutes,whereby a 2-n-butoxyethanol solution of 1 mol/kg tungsten pentaethoxidewas obtained.

[6-1-5] Preparation of 2-n-Butoxyethanol Solution of NiobiumPentaethoxide

In a 20-g reagent bottle made of Pyrex equipped with a magnetic stirringbar, 3.1821 g of niobium pentaethoxide (4N, manufactured by KojundoChemical Lab. Co., Ltd.) and 6.8179 g of 2-n-butoxyethanol (Cica SpecialGrade, manufactured by Kanto Chemical Co., Inc.) were weighed. Then, thereagent bottle was placed on a hot plate with a magnetic stirrerfunction, and niobium pentaethoxide was completely dissolved in2-n-butoxyethanol while stirring at room temperature for 30 minutes,whereby a 2-n-butoxyethanol solution of 1 mol/kg niobium pentaethoxidewas obtained.

[6-1-6] Preparation of 2-n-Butoxyethanol Solution of TantalumPentaethoxide

In a 20-g reagent bottle made of Pyrex equipped with a magnetic stirringbar, 4.0626 g of tantalum pentaethoxide (5N, manufactured by KojundoChemical Lab. Co., Ltd.) and 5.9374 g of 2-n-butoxyethanol (Cica SpecialGrade, manufactured by Kanto Chemical Co., Inc.) were weighed. Then, thereagent bottle was placed on a hot plate with a magnetic stirrerfunction, and tantalum pentaethoxide was completely dissolved in2-n-butoxyethanol while stirring at room temperature for 30 minutes,whereby a 2-n-butoxyethanol solution of 1 mol/kg tantalum pentaethoxidewas obtained.

[6-1-7] Preparation of 2-n-Butoxyethanol Solution of Antimonytri-n-Butoxide

In a 20-g reagent bottle made of Pyrex equipped with a magnetic stirringbar, 3.4110 g of antimony tri-n-butoxide (manufactured by Wako PureChemical Industries, Ltd.) and 6.5890 g of 2-n-butoxyethanol (CicaSpecial Grade, manufactured by Kanto Chemical Co., Inc.) were weighed.Then, the reagent bottle was placed on a hot plate with a magneticstirrer function, and antimony tri-n-butoxide was completely dissolvedin 2-n-butoxyethanol while stirring at room temperature for 30 minutes,whereby a 2-n-butoxyethanol solution of 1 mol/kg antimony tri-n-butoxidewas obtained.

[6-2] Production of Calcined Bodies According to Respective Examples andComparative Examples

By using the respective metal compound solutions obtained as describedabove, calcined bodies according to the respective Examples and therespective Comparative Examples were produced as follows.

Example 1

In this Example, a calcined body to be used in the production of a solidelectrolyte represented by the formulation:Li_(6.15)La₃(Zr_(1.5)W_(0.35)Ta_(0.15))O₁₂ was produced as follows.

First, in a reagent bottle made of Pyrex, 7.380 g of a 2-n-butoxyethanolsolution of lithium nitrate and 3.000 g of a 2-n-butoxyethanol solutionof lanthanum nitrate hexahydrate, each of which was prepared asdescribed above, and 2 mL of 2-n-butoxyethanol as an organic solventwere weighed. A magnetic stirring bar was put therein, and the reagentbottle was placed on a hot plate with a magnetic stirrer function.

Heating and stirring were performed for 30 minutes by setting the settemperature of the hot plate to 160° C. and the rotation speed to 500rpm.

Subsequently, 2 mL of 2-n-butoxyethanol was added thereto, and heatingand stirring were performed again for 30 minutes. When 30 minute-heatingand stirring is regarded as a one-time dehydration treatment, in thisExample, a dehydration treatment is regarded as having been performedtwice.

After the dehydration treatment, the reagent bottle was covered with alid and sealed.

Subsequently, stirring was performed by setting the set temperature ofthe hot plate to 25° C. and the rotation speed to 500 rpm, therebygradually cooling the reaction mixture to room temperature.

Subsequently, the reagent bottle was transferred to a dry atmosphere,and in the reagent bottle, 1.500 g of a 2-n-butoxyethanol solution ofzirconium tetra-n-butoxide, 0.350 g of a 2-n-butoxyethanol solution oftungsten pentaethoxide, and 0.150 g of a 2-n-butoxyethanol solution oftantalum pentaethoxide, each of which was prepared as described above,were weighed. A magnetic stirring bar was put therein.

Subsequently, stirring was performed at room temperature for 30 minutesby setting the rotation speed of a magnetic stirrer to 500 rpm, wherebya precursor solution was obtained.

Subsequently, the obtained precursor solution was placed in a dish madeof titanium having an inner diameter of 50 mm and a height of 20 mm.This dish was placed on a hot plate and heated for 1 hour by setting theset temperature of the hot plate to 160° C., and then heated for 30minutes by setting the set temperature of the hot plate to 180° C.,thereby removing the solvent.

Subsequently, the dish was heated for 30 minutes by setting the settemperature of the hot plate to 360° C., thereby decomposing most of thecontained organic components by combustion.

Thereafter, the dish was heated for 1 hour by setting the settemperature of the hot plate to 540° C., thereby burning and decomposingthe remaining organic components. Then, the dish was gradually cooled toroom temperature on the hot plate, whereby a solid composition as thecalcined body was obtained.

Example 2

In this Example, a calcined body to be used in the production of a solidelectrolyte represented by the formulation:Li_(6.15)La₃(Zr_(1.5)W_(0.35)Nb_(0.15))O₁₂ was produced as follows.

First, in a reagent bottle made of Pyrex, 7.380 g of a 2-n-butoxyethanolsolution of lithium nitrate and 3.000 g of a 2-n-butoxyethanol solutionof lanthanum nitrate hexahydrate, each of which was prepared asdescribed above, and 2 mL of 2-n-butoxyethanol as an organic solventwere weighed. A magnetic stirring bar was put therein, and the reagentbottle was placed on a hot plate with a magnetic stirrer function.

Heating and stirring were performed for 30 minutes by setting the settemperature of the hot plate to 160° C. and the rotation speed to 500rpm.

Subsequently, 2 mL of 2-n-butoxyethanol was added thereto, and heatingand stirring were performed again for 30 minutes. When 30 minute-heatingand stirring is regarded as a one-time dehydration treatment, in thisExample, a dehydration treatment is regarded as having been performedtwice.

After the dehydration treatment, the reagent bottle was covered with alid and sealed.

Subsequently, stirring was performed by setting the set temperature ofthe hot plate to 25° C. and the rotation speed to 500 rpm, therebygradually cooling the reaction mixture to room temperature.

Subsequently, the reagent bottle was transferred to a dry atmosphere,and in the reagent bottle, 1.500 g of a 2-n-butoxyethanol solution ofzirconium tetra-n-butoxide, 0.350 g of a 2-n-butoxyethanol solution oftungsten pentaethoxide, and 0.150 g of a 2-n-butoxyethanol solution ofniobium pentaethoxide, each of which was prepared as described above,were weighed. A magnetic stirring bar was put therein.

Subsequently, stirring was performed at room temperature for 30 minutesby setting the rotation speed of a magnetic stirrer to 500 rpm, wherebya precursor solution was obtained.

Subsequently, the obtained precursor solution was placed in a dish madeof titanium having an inner diameter of 50 mm and a height of 20 mm.This dish was placed on a hot plate and heated for 1 hour by setting theset temperature of the hot plate to 160° C., and then heated for 30minutes by setting the set temperature of the hot plate to 180° C.,thereby removing the solvent.

Subsequently, the dish was heated for 30 minutes by setting the settemperature of the hot plate to 360° C., thereby decomposing most of thecontained organic components by combustion.

Thereafter, the dish was heated for 1 hour by setting the settemperature of the hot plate to 540° C., thereby burning and decomposingthe remaining organic components. Then, the dish was gradually cooled toroom temperature on the hot plate, whereby a solid composition as thecalcined body was obtained.

Example 3

In this Example, a calcined body to be used in the production of a solidelectrolyte represented by the formulation:Li_(6.15)La₃(Zr_(1.5)W_(0.35)Sb_(0.15))O₁₂ was produced as follows.

First, in a reagent bottle made of Pyrex, 7.380 g of a 2-n-butoxyethanolsolution of lithium nitrate and 3.000 g of a 2-n-butoxyethanol solutionof lanthanum nitrate hexahydrate, each of which was prepared asdescribed above, and 2 mL of 2-n-butoxyethanol as an organic solventwere weighed. A magnetic stirring bar was put therein, and the reagentbottle was placed on a hot plate with a magnetic stirrer function.

Heating and stirring were performed for 30 minutes by setting the settemperature of the hot plate to 160° C. and the rotation speed to 500rpm.

Subsequently, 2 mL of 2-n-butoxyethanol was added thereto, and heatingand stirring were performed again for 30 minutes. When 30 minute-heatingand stirring is regarded as a one-time dehydration treatment, in thisExample, a dehydration treatment is regarded as having been performedtwice.

After the dehydration treatment, the reagent bottle was covered with alid and sealed.

Subsequently, stirring was performed by setting the set temperature ofthe hot plate to 25° C. and the rotation speed to 500 rpm, therebygradually cooling the reaction mixture to room temperature.

Subsequently, the reagent bottle was transferred to a dry atmosphere,and in the reagent bottle, 1.500 g of a 2-n-butoxyethanol solution ofzirconium tetra-n-butoxide, 0.350 g of a 2-n-butoxyethanol solution oftungsten pentaethoxide, and 0.150 g of a 2-n-butoxyethanol solution ofantimony tri-n-butoxide, each of which was prepared as described above,were weighed. A magnetic stirring bar was put therein.

Subsequently, stirring was performed at room temperature for 30 minutesby setting the rotation speed of a magnetic stirrer to 500 rpm, wherebya precursor solution was obtained.

Subsequently, the obtained precursor solution was placed in a dish madeof titanium having an inner diameter of 50 mm and a height of 20 mm.This dish was placed on a hot plate and heated for 1 hour by setting theset temperature of the hot plate to 160° C., and then heated for 30minutes by setting the set temperature of the hot plate to 180° C.,thereby removing the solvent.

Subsequently, the dish was heated for 30 minutes by setting the settemperature of the hot plate to 360° C., thereby decomposing most of thecontained organic components by combustion.

Thereafter, the dish was heated for 1 hour by setting the settemperature of the hot plate to 540° C., thereby burning and decomposingthe remaining organic components. Then, the dish was gradually cooled toroom temperature on the hot plate, whereby a solid composition as thecalcined body was obtained.

Example 4

In this Example, a calcined body to be used in the production of a solidelectrolyte represented by the formulation:Li_(5.75)La₃(Zr_(1.35)W_(0.6)Nb_(0.05))O₁₂ was produced as follows.

First, in a reagent bottle made of Pyrex, 6.900 g of a 2-n-butoxyethanolsolution of lithium nitrate and 3.000 g of a 2-n-butoxyethanol solutionof lanthanum nitrate hexahydrate, each of which was prepared asdescribed above, and 2 mL of 2-n-butoxyethanol as an organic solventwere weighed. A magnetic stirring bar was put therein, and the reagentbottle was placed on a hot plate with a magnetic stirrer function.

Heating and stirring were performed for 30 minutes by setting the settemperature of the hot plate to 160° C. and the rotation speed to 500rpm.

Subsequently, 2 mL of 2-n-butoxyethanol was added thereto, and heatingand stirring were performed again for 30 minutes. When 30 minute-heatingand stirring is regarded as a one-time dehydration treatment, in thisExample, a dehydration treatment is regarded as having been performedtwice.

After the dehydration treatment, the reagent bottle was covered with alid and sealed.

Subsequently, stirring was performed by setting the set temperature ofthe hot plate to 25° C. and the rotation speed to 500 rpm, therebygradually cooling the reaction mixture to room temperature.

Subsequently, the reagent bottle was transferred to a dry atmosphere,and in the reagent bottle, 1.350 g of a 2-n-butoxyethanol solution ofzirconium tetra-n-butoxide, 0.600 g of a 2-n-butoxyethanol solution oftungsten pentaethoxide, and 0.050 g of a 2-n-butoxyethanol solution ofniobium pentaethoxide, each of which was prepared as described above,were weighed. A magnetic stirring bar was put therein.

Subsequently, stirring was performed at room temperature for 30 minutesby setting the rotation speed of a magnetic stirrer to 500 rpm, wherebya precursor solution was obtained.

Subsequently, the obtained precursor solution was placed in a dish madeof titanium having an inner diameter of 50 mm and a height of 20 mm.This dish was placed on a hot plate and heated for 1 hour by setting theset temperature of the hot plate to 160° C., and then heated for 30minutes by setting the set temperature of the hot plate to 180° C.,thereby removing the solvent.

Subsequently, the dish was heated for 30 minutes by setting the settemperature of the hot plate to 360° C., thereby decomposing most of thecontained organic components by combustion.

Thereafter, the dish was heated for 1 hour by setting the settemperature of the hot plate to 540° C., thereby burning and decomposingthe remaining organic components. Then, the dish was gradually cooled toroom temperature on the hot plate, whereby a solid composition as thecalcined body was obtained.

Example 5

In this Example, a calcined body to be used in the production of a solidelectrolyte represented by the formulation:Li_(6.55)La₃(Zr_(1.65)W_(0.1)Ta_(0.25))O₁₂ was produced as follows.

First, in a reagent bottle made of Pyrex, 7.860 g of a 2-n-butoxyethanolsolution of lithium nitrate and 3.000 g of a 2-n-butoxyethanol solutionof lanthanum nitrate hexahydrate, each of which was prepared asdescribed above, and 2 mL of 2-n-butoxyethanol as an organic solventwere weighed. A magnetic stirring bar was put therein, and the reagentbottle was placed on a hot plate with a magnetic stirrer function.

Heating and stirring were performed for 30 minutes by setting the settemperature of the hot plate to 160° C. and the rotation speed to 500rpm.

Subsequently, 2 mL of 2-n-butoxyethanol was added thereto, and heatingand stirring were performed again for 30 minutes. When 30 minute-heatingand stirring is regarded as a one-time dehydration treatment, in thisExample, a dehydration treatment is regarded as having been performedtwice.

After the dehydration treatment, the reagent bottle was covered with alid and sealed.

Subsequently, stirring was performed by setting the set temperature ofthe hot plate to 25° C. and the rotation speed to 500 rpm, therebygradually cooling the reaction mixture to room temperature.

Subsequently, the reagent bottle was transferred to a dry atmosphere,and in the reagent bottle, 1.650 g of a 2-n-butoxyethanol solution ofzirconium tetra-n-butoxide, 0.100 g of a 2-n-butoxyethanol solution oftungsten pentaethoxide, and 0.250 g of a 2-n-butoxyethanol solution oftantalum pentaethoxide, each of which was prepared as described above,were weighed. A magnetic stirring bar was put therein.

Subsequently, stirring was performed at room temperature for 30 minutesby setting the rotation speed of a magnetic stirrer to 500 rpm, wherebya precursor solution was obtained.

Subsequently, the obtained precursor solution was placed in a dish madeof titanium having an inner diameter of 50 mm and a height of 20 mm.This dish was placed on a hot plate and heated for 1 hour by setting theset temperature of the hot plate to 160° C., and then heated for 30minutes by setting the set temperature of the hot plate to 180° C.,thereby removing the solvent.

Subsequently, the dish was heated for 30 minutes by setting the settemperature of the hot plate to 360° C., thereby decomposing most of thecontained organic components by combustion.

Thereafter, the dish was heated for 1 hour by setting the settemperature of the hot plate to 540° C., thereby burning and decomposingthe remaining organic components. Then, the dish was gradually cooled toroom temperature on the hot plate, whereby a solid composition as thecalcined body was obtained.

Example 6

In this Example, a calcined body to be used in the production of a solidelectrolyte represented by the formulation:Li_(6.4)La₃(Zr_(1.65)W_(0.25)Sb_(0.1))O₁₂ was produced as follows.

First, in a reagent bottle made of Pyrex, 7.680 g of a 2-n-butoxyethanolsolution of lithium nitrate and 3.000 g of a 2-n-butoxyethanol solutionof lanthanum nitrate hexahydrate, each of which was prepared asdescribed above, and 2 mL of 2-n-butoxyethanol as an organic solventwere weighed. A magnetic stirring bar was put therein, and the reagentbottle was placed on a hot plate with a magnetic stirrer function.

Heating and stirring were performed for 30 minutes by setting the settemperature of the hot plate to 160° C. and the rotation speed to 500rpm.

Subsequently, 2 mL of 2-n-butoxyethanol was added thereto, and heatingand stirring were performed again for 30 minutes. When 30 minute-heatingand stirring is regarded as a one-time dehydration treatment, in thisExample, a dehydration treatment is regarded as having been performedtwice.

After the dehydration treatment, the reagent bottle was covered with alid and sealed.

Subsequently, stirring was performed by setting the set temperature ofthe hot plate to 25° C. and the rotation speed to 500 rpm, therebygradually cooling the reaction mixture to room temperature.

Subsequently, the reagent bottle was transferred to a dry atmosphere,and in the reagent bottle, 1.650 g of a 2-n-butoxyethanol solution ofzirconium tetra-n-butoxide, 0.250 g of a 2-n-butoxyethanol solution oftungsten pentaethoxide, and 0.100 g of a 2-n-butoxyethanol solution ofantimony tri-n-butoxide, each of which was prepared as described above,were weighed. A magnetic stirring bar was put therein.

Subsequently, stirring was performed at room temperature for 30 minutesby setting the rotation speed of a magnetic stirrer to 500 rpm, wherebya precursor solution was obtained.

Subsequently, the obtained precursor solution was placed in a dish madeof titanium having an inner diameter of 50 mm and a height of 20 mm.This dish was placed on a hot plate and heated for 1 hour by setting theset temperature of the hot plate to 160° C., and then heated for 30minutes by setting the set temperature of the hot plate to 180° C.,thereby removing the solvent.

Subsequently, the dish was heated for 30 minutes by setting the settemperature of the hot plate to 360° C., thereby decomposing most of thecontained organic components by combustion.

Thereafter, the dish was heated for 1 hour by setting the settemperature of the hot plate to 540° C., thereby burning and decomposingthe remaining organic components. Then, the dish was gradually cooled toroom temperature on the hot plate, whereby a solid composition as thecalcined body was obtained.

Example 7

In this Example, a calcined body to be used in the production of a solidelectrolyte represented by the formulation:Li_(6.15)La₃(Zr_(1.5)W_(0.35)Nb_(0.13)Ta_(0.02))O₁₂ was produced asfollows.

First, in a reagent bottle made of Pyrex, 7.380 g of a 2-n-butoxyethanolsolution of lithium nitrate and 3.000 g of a 2-n-butoxyethanol solutionof lanthanum nitrate hexahydrate, each of which was prepared asdescribed above, and 2 mL of 2-n-butoxyethanol as an organic solventwere weighed. A magnetic stirring bar was put therein, and the reagentbottle was placed on a hot plate with a magnetic stirrer function.

Heating and stirring were performed for 30 minutes by setting the settemperature of the hot plate to 160° C. and the rotation speed to 500rpm.

Subsequently, 2 mL of 2-n-butoxyethanol was added thereto, and heatingand stirring were performed again for 30 minutes. When 30 minute-heatingand stirring is regarded as a one-time dehydration treatment, in thisExample, a dehydration treatment is regarded as having been performedtwice.

After the dehydration treatment, the reagent bottle was covered with alid and sealed.

Subsequently, stirring was performed by setting the set temperature ofthe hot plate to 25° C. and the rotation speed to 500 rpm, therebygradually cooling the reaction mixture to room temperature.

Subsequently, the reagent bottle was transferred to a dry atmosphere,and in the reagent bottle, 1.500 g of a 2-n-butoxyethanol solution ofzirconium tetra-n-butoxide, 0.350 g of a 2-n-butoxyethanol solution oftungsten pentaethoxide, 0.130 g of a 2-n-butoxyethanol solution ofniobium pentaethoxide, and 0.020 g of a 2-n-butoxyethanol solution oftantalum pentaethoxide, each of which was prepared as described above,were weighed. A magnetic stirring bar was put therein.

Subsequently, stirring was performed at room temperature for 30 minutesby setting the rotation speed of a magnetic stirrer to 500 rpm, wherebya precursor solution was obtained.

Subsequently, the obtained precursor solution was placed in a dish madeof titanium having an inner diameter of 50 mm and a height of 20 mm.This dish was placed on a hot plate and heated for 1 hour by setting theset temperature of the hot plate to 160° C., and then heated for 30minutes by setting the set temperature of the hot plate to 180° C.,thereby removing the solvent.

Subsequently, the dish was heated for 30 minutes by setting the settemperature of the hot plate to 360° C., thereby decomposing most of thecontained organic components by combustion.

Thereafter, the dish was heated for 1 hour by setting the settemperature of the hot plate to 540° C., thereby burning and decomposingthe remaining organic components. Then, the dish was gradually cooled toroom temperature on the hot plate, whereby a solid composition as thecalcined body was obtained.

Example 8

In this Example, a calcined body to be used in the production of a solidelectrolyte represented by the formulation:Li_(6.75)La₃(Zr_(1.85)W_(0.10)Nb_(0.05))O₁₂ was produced as follows.

First, in a reagent bottle made of Pyrex, 8.100 g of a 2-n-butoxyethanolsolution of lithium nitrate and 3.000 g of a 2-n-butoxyethanol solutionof lanthanum nitrate hexahydrate, each of which was prepared asdescribed above, and 2 mL of 2-n-butoxyethanol as an organic solventwere weighed. A magnetic stirring bar was put therein, and the reagentbottle was placed on a hot plate with a magnetic stirrer function.

Heating and stirring were performed for 30 minutes by setting the settemperature of the hot plate to 160° C. and the rotation speed to 500rpm.

Subsequently, 2 mL of 2-n-butoxyethanol was added thereto, and heatingand stirring were performed again for 30 minutes. When 30 minute-heatingand stirring is regarded as a one-time dehydration treatment, in thisExample, a dehydration treatment is regarded as having been performedtwice.

After the dehydration treatment, the reagent bottle was covered with alid and sealed.

Subsequently, stirring was performed by setting the set temperature ofthe hot plate to 25° C. and the rotation speed to 500 rpm, therebygradually cooling the reaction mixture to room temperature.

Subsequently, the reagent bottle was transferred to a dry atmosphere,and in the reagent bottle, 1.850 g of a 2-n-butoxyethanol solution ofzirconium tetra-n-butoxide, 0.100 g of a 2-n-butoxyethanol solution oftungsten pentaethoxide, and 0.050 g of a 2-n-butoxyethanol solution ofniobium pentaethoxide, each of which was prepared as described above,were weighed. A magnetic stirring bar was put therein.

Subsequently, stirring was performed at room temperature for 30 minutesby setting the rotation speed of a magnetic stirrer to 500 rpm, wherebya precursor solution was obtained.

Subsequently, the obtained precursor solution was placed in a dish madeof titanium having an inner diameter of 50 mm and a height of 20 mm.This dish was placed on a hot plate and heated for 1 hour by setting theset temperature of the hot plate to 160° C., and then heated for 30minutes by setting the set temperature of the hot plate to 180° C.,thereby removing the solvent.

Subsequently, the dish was heated for 30 minutes by setting the settemperature of the hot plate to 360° C., thereby decomposing most of thecontained organic components by combustion.

Thereafter, the dish was heated for 1 hour by setting the settemperature of the hot plate to 540° C., thereby burning and decomposingthe remaining organic components. Then, the dish was gradually cooled toroom temperature on the hot plate, whereby a solid composition as thecalcined body was obtained.

Example 9

In this Example, a calcined body to be used in the production of a solidelectrolyte represented by the formulation:Li_(5.59)La₃(Zr_(1.17)W_(0.58)Sb_(0.25))O₁₂ was produced as follows.

First, in a reagent bottle made of Pyrex, 6.708 g of a 2-n-butoxyethanolsolution of lithium nitrate and 3.000 g of a 2-n-butoxyethanol solutionof lanthanum nitrate hexahydrate, each of which was prepared asdescribed above, and 2 mL of 2-n-butoxyethanol as an organic solventwere weighed. A magnetic stirring bar was put therein, and the reagentbottle was placed on a hot plate with a magnetic stirrer function.

Heating and stirring were performed for 30 minutes by setting the settemperature of the hot plate to 160° C. and the rotation speed to 500rpm.

Subsequently, 2 mL of 2-n-butoxyethanol was added thereto, and heatingand stirring were performed again for 30 minutes. When 30 minute-heatingand stirring is regarded as a one-time dehydration treatment, in thisExample, a dehydration treatment is regarded as having been performedtwice.

After the dehydration treatment, the reagent bottle was covered with alid and sealed.

Subsequently, stirring was performed by setting the set temperature ofthe hot plate to 25° C. and the rotation speed to 500 rpm, therebygradually cooling the reaction mixture to room temperature.

Subsequently, the reagent bottle was transferred to a dry atmosphere,and in the reagent bottle, 1.170 g of a 2-n-butoxyethanol solution ofzirconium tetra-n-butoxide, 0.580 g of a 2-n-butoxyethanol solution oftungsten pentaethoxide, and 0.250 g of a 2-n-butoxyethanol solution ofantimony tri-n-butoxide, each of which was prepared as described above,were weighed. A magnetic stirring bar was put therein.

Subsequently, stirring was performed at room temperature for 30 minutesby setting the rotation speed of a magnetic stirrer to 500 rpm, wherebya precursor solution was obtained.

Subsequently, the obtained precursor solution was placed in a dish madeof titanium having an inner diameter of 50 mm and a height of 20 mm.This dish was placed on a hot plate and heated for 1 hour by setting theset temperature of the hot plate to 160° C., and then heated for 30minutes by setting the set temperature of the hot plate to 180° C.,thereby removing the solvent.

Subsequently, the dish was heated for 30 minutes by setting the settemperature of the hot plate to 360° C., thereby decomposing most of thecontained organic components by combustion.

Thereafter, the dish was heated for 1 hour by setting the settemperature of the hot plate to 540° C., thereby burning and decomposingthe remaining organic components. Then, the dish was gradually cooled toroom temperature on the hot plate, whereby a solid composition as thecalcined body was obtained.

Comparative Example 1

In this Comparative Example, a calcined body to be used in theproduction of a solid electrolyte represented by the formulation:Li_(60.1)La₃ (Zr_(1.5)W_(0.45))O₁₂ was produced as follows.

First, in a reagent bottle made of Pyrex, 7.320 g of a 2-n-butoxyethanolsolution of lithium nitrate and 3.000 g of a 2-n-butoxyethanol solutionof lanthanum nitrate hexahydrate, each of which was prepared asdescribed above, and 2 mL of 2-n-butoxyethanol as an organic solventwere weighed. A magnetic stirring bar was put therein, and the reagentbottle was placed on a hot plate with a magnetic stirrer function.

Heating and stirring were performed for 30 minutes by setting the settemperature of the hot plate to 160° C. and the rotation speed to 500rpm.

Subsequently, 2 mL of 2-n-butoxyethanol was added thereto, and heatingand stirring were performed again for 30 minutes. When 30 minute-heatingand stirring is regarded as a one-time dehydration treatment, in thisComparative Example, a dehydration treatment is regarded as having beenperformed twice.

After the dehydration treatment, the reagent bottle was covered with alid and sealed.

Subsequently, stirring was performed by setting the set temperature ofthe hot plate to 25° C. and the rotation speed to 500 rpm, therebygradually cooling the reaction mixture to room temperature.

Subsequently, the reagent bottle was transferred to a dry atmosphere,and in the reagent bottle, 1.500 g of a 2-n-butoxyethanol solution ofzirconium tetra-n-butoxide and 0.450 g of a 2-n-butoxyethanol solutionof tungsten pentaethoxide, each of which was prepared as describedabove, were weighed. A magnetic stirring bar was put therein.

Subsequently, stirring was performed at room temperature for 30 minutesby setting the rotation speed of a magnetic stirrer to 500 rpm, wherebya precursor solution was obtained.

Subsequently, the obtained precursor solution was placed in a dish madeof titanium having an inner diameter of 50 mm and a height of 20 mm.This dish was placed on a hot plate and heated for 1 hour by setting theset temperature of the hot plate to 160° C., and then heated for 30minutes by setting the set temperature of the hot plate to 180° C.,thereby removing the solvent.

Subsequently, the dish was heated for 30 minutes by setting the settemperature of the hot plate to 360° C., thereby decomposing most of thecontained organic components by combustion.

Thereafter, the dish was heated for 1 hour by setting the settemperature of the hot plate to 540° C., thereby burning and decomposingthe remaining organic components. Then, the dish was gradually cooled toroom temperature on the hot plate, whereby a solid composition as thecalcined body was obtained.

Comparative Example 2

In this Comparative Example, a calcined body to be used in theproduction of a solid electrolyte represented by the formulation:Li_(6.75)La₃(Zr_(1.6)W_(0.05)Ta_(0.15))O₁₂ was produced as follows.

First, in a reagent bottle made of Pyrex, 8.100 g of a 2-n-butoxyethanolsolution of lithium nitrate and 3.000 g of a 2-n-butoxyethanol solutionof lanthanum nitrate hexahydrate, each of which was prepared asdescribed above, and 2 mL of 2-n-butoxyethanol as an organic solventwere weighed. A magnetic stirring bar was put therein, and the reagentbottle was placed on a hot plate with a magnetic stirrer function.

Heating and stirring were performed for 30 minutes by setting the settemperature of the hot plate to 160° C. and the rotation speed to 500rpm.

Subsequently, 2 mL of 2-n-butoxyethanol was added thereto, and heatingand stirring were performed again for 30 minutes. When 30 minute-heatingand stirring is regarded as a one-time dehydration treatment, in thisComparative Example, a dehydration treatment is regarded as having beenperformed twice.

After the dehydration treatment, the reagent bottle was covered with alid and sealed.

Subsequently, stirring was performed by setting the set temperature ofthe hot plate to 25° C. and the rotation speed to 500 rpm, therebygradually cooling the reaction mixture to room temperature.

Subsequently, the reagent bottle was transferred to a dry atmosphere,and in the reagent bottle, 1.800 g of a 2-n-butoxyethanol solution ofzirconium tetra-n-butoxide, 0.050 g of a 2-n-butoxyethanol solution oftungsten pentaethoxide, and 0.150 g of a 2-n-butoxyethanol solution oftantalum pentaethoxide, each of which was prepared as described above,were weighed. A magnetic stirring bar was put therein.

Subsequently, stirring was performed at room temperature for 30 minutesby setting the rotation speed of a magnetic stirrer to 500 rpm, wherebya precursor solution was obtained.

Subsequently, the obtained precursor solution was placed in a dish madeof titanium having an inner diameter of 50 mm and a height of 20 mm.This dish was placed on a hot plate and heated for 1 hour by setting theset temperature of the hot plate to 160° C., and then heated for 30minutes by setting the set temperature of the hot plate to 180° C.,thereby removing the solvent.

Subsequently, the dish was heated for 30 minutes by setting the settemperature of the hot plate to 360° C., thereby decomposing most of thecontained organic components by combustion.

Thereafter, the dish was heated for 1 hour by setting the settemperature of the hot plate to 540° C., thereby burning and decomposingthe remaining organic components. Then, the dish was gradually cooled toroom temperature on the hot plate, whereby a solid composition as thecalcined body was obtained.

Comparative Example 3

In this Comparative Example, a calcined body to be used in theproduction of a solid electrolyte represented by the formulation:Li₆La₃(Zr_(1.35)W_(0.35)Sb_(0.3))O₁₂ was produced as follows.

First, in a reagent bottle made of Pyrex, 7.200 g of a 2-n-butoxyethanolsolution of lithium nitrate and 3.000 g of a 2-n-butoxyethanol solutionof lanthanum nitrate hexahydrate, each of which was prepared asdescribed above, and 2 mL of 2-n-butoxyethanol as an organic solventwere weighed. A magnetic stirring bar was put therein, and the reagentbottle was placed on a hot plate with a magnetic stirrer function.

Heating and stirring were performed for 30 minutes by setting the settemperature of the hot plate to 160° C. and the rotation speed to 500rpm.

Subsequently, 2 mL of 2-n-butoxyethanol was added thereto, and heatingand stirring were performed again for 30 minutes. When 30 minute-heatingand stirring is regarded as a one-time dehydration treatment, in thisComparative Example, a dehydration treatment is regarded as having beenperformed twice.

After the dehydration treatment, the reagent bottle was covered with alid and sealed.

Subsequently, stirring was performed by setting the set temperature ofthe hot plate to 25° C. and the rotation speed to 500 rpm, therebygradually cooling the reaction mixture to room temperature.

Subsequently, the reagent bottle was transferred to a dry atmosphere,and in the reagent bottle, 1.350 g of a 2-n-butoxyethanol solution ofzirconium tetra-n-butoxide, 0.350 g of a 2-n-butoxyethanol solution oftungsten pentaethoxide, and 0.300 g of a 2-n-butoxyethanol solution ofantimony tri-n-butoxide, each of which was prepared as described above,were weighed. A magnetic stirring bar was put therein.

Subsequently, stirring was performed at room temperature for 30 minutesby setting the rotation speed of a magnetic stirrer to 500 rpm, wherebya precursor solution was obtained.

Subsequently, the obtained precursor solution was placed in a dish madeof titanium having an inner diameter of 50 mm and a height of 20 mm.This dish was placed on a hot plate and heated for 1 hour by setting theset temperature of the hot plate to 160° C., and then heated for 30minutes by setting the set temperature of the hot plate to 180° C.,thereby removing the solvent.

Subsequently, the dish was heated for 30 minutes by setting the settemperature of the hot plate to 360° C., thereby decomposing most of thecontained organic components by combustion.

Thereafter, the dish was heated for 1 hour by setting the settemperature of the hot plate to 540° C., thereby burning and decomposingthe remaining organic components. Then, the dish was gradually cooled toroom temperature on the hot plate, whereby a solid composition as thecalcined body was obtained.

Comparative Example 4

In this Comparative Example, a calcined body to be used in theproduction of a solid electrolyte represented by the formulation:Li_(5.4)La₃(Zr_(1.05)W_(0.65)Nb_(0.3))O₁₂ was produced as follows.

First, in a reagent bottle made of Pyrex, 6.480 g of a 2-n-butoxyethanolsolution of lithium nitrate and 3.000 g of a 2-n-butoxyethanol solutionof lanthanum nitrate hexahydrate, each of which was prepared asdescribed above, and 2 mL of 2-n-butoxyethanol as an organic solventwere weighed. A magnetic stirring bar was put therein, and the reagentbottle was placed on a hot plate with a magnetic stirrer function.

Heating and stirring were performed for 30 minutes by setting the settemperature of the hot plate to 160° C. and the rotation speed to 500rpm.

Subsequently, 2 mL of 2-n-butoxyethanol was added thereto, and heatingand stirring were performed again for 30 minutes. When 30 minute-heatingand stirring is regarded as a one-time dehydration treatment, in thisComparative Example, a dehydration treatment is regarded as having beenperformed twice.

After the dehydration treatment, the reagent bottle was covered with alid and sealed.

Subsequently, stirring was performed by setting the set temperature ofthe hot plate to 25° C. and the rotation speed to 500 rpm, therebygradually cooling the reaction mixture to room temperature.

Subsequently, the reagent bottle was transferred to a dry atmosphere,and in the reagent bottle, 1.050 g of a 2-n-butoxyethanol solution ofzirconium tetra-n-butoxide, 0.650 g of a 2-n-butoxyethanol solution oftungsten pentaethoxide, and 0.300 g of a 2-n-butoxyethanol solution ofniobium pentaethoxide, each of which was prepared as described above,were weighed. A magnetic stirring bar was put therein.

Subsequently, stirring was performed at room temperature for 30 minutesby setting the rotation speed of a magnetic stirrer to 500 rpm, wherebya precursor solution was obtained.

Subsequently, the obtained precursor solution was placed in a dish madeof titanium having an inner diameter of 50 mm and a height of 20 mm.This dish was placed on a hot plate and heated for 1 hour by setting theset temperature of the hot plate to 160° C., and then heated for 30minutes by setting the set temperature of the hot plate to 180° C.,thereby removing the solvent.

Subsequently, the dish was heated for 30 minutes by setting the settemperature of the hot plate to 360° C., thereby decomposing most of thecontained organic components by combustion.

Thereafter, the dish was heated for 1 hour by setting the settemperature of the hot plate to 540° C., thereby burning and decomposingthe remaining organic components. Then, the dish was gradually cooled toroom temperature on the hot plate, whereby a solid composition as thecalcined body was obtained.

Comparative Example 5

In this Comparative Example, a calcined body to be used in theproduction of a solid electrolyte represented by the formulation:Li_(6.75)La₃(Zr_(1.75)Nb_(0.25))O₁₂ was produced as follows.

First, in a reagent bottle made of Pyrex, 8.775 g of a 2-n-butoxyethanolsolution of lithium nitrate and 3.000 g of a 2-n-butoxyethanol solutionof lanthanum nitrate hexahydrate, each of which was prepared asdescribed above, and 2 mL of 2-n-butoxyethanol as an organic solventwere weighed. A magnetic stirring bar was put therein, and the reagentbottle was placed on a hot plate with a magnetic stirrer function.

Heating and stirring were performed for 30 minutes by setting the settemperature of the hot plate to 160° C. and the rotation speed to 500rpm.

Subsequently, 2 mL of 2-n-butoxyethanol was added thereto, and heatingand stirring were performed again for 30 minutes. When 30 minute-heatingand stirring is regarded as a one-time dehydration treatment, in thisComparative Example, a dehydration treatment is regarded as having beenperformed twice.

After the dehydration treatment, the reagent bottle was covered with alid and sealed.

Subsequently, stirring was performed by setting the set temperature ofthe hot plate to 25° C. and the rotation speed to 500 rpm, therebygradually cooling the reaction mixture to room temperature.

Subsequently, the reagent bottle was transferred to a dry atmosphere,and in the reagent bottle, 1.750 g of a 2-n-butoxyethanol solution ofzirconium tetra-n-butoxide and 0.250 g of a 2-n-butoxyethanol solutionof niobium pentaethoxide, each of which was prepared as described above,were weighed. A magnetic stirring bar was put therein.

Subsequently, stirring was performed at room temperature for 30 minutesby setting the rotation speed of a magnetic stirrer to 500 rpm, wherebya precursor solution was obtained.

Subsequently, the obtained precursor solution was placed in a dish madeof titanium having an inner diameter of 50 mm and a height of 20 mm.This dish was placed on a hot plate and heated for 1 hour by setting theset temperature of the hot plate to 160° C., and then heated for 30minutes by setting the set temperature of the hot plate to 180° C.,thereby removing the solvent.

Subsequently, the dish was heated for 30 minutes by setting the settemperature of the hot plate to 360° C., thereby decomposing most of thecontained organic components by combustion.

Thereafter, the dish was heated for 1 hour by setting the settemperature of the hot plate to 540° C., thereby burning and decomposingthe remaining organic components. Then, the dish was gradually cooled toroom temperature on the hot plate, whereby a solid composition as thecalcined body was obtained.

[6-3] Production of Solid Electrolyte

Solid electrolytes were produced as follows using the calcined bodiesaccording to the respective Examples and the respective ComparativeExamples obtained as described above, respectively.

First, the calcined body was transferred to an agate mortar andsufficiently ground. A 0.150 g portion of the thus obtained groundmaterial of the calcined body was weighed out and placed in a pellet diewith an exhaust port having an inner diameter of 10 mm as a molding die,pressed at a pressure of 0.624 kN/mm² for 5 minutes, whereby a calcinedbody pellet that is a disk-shaped molded material was produced.

Then, the calcined body pellet was placed in a crucible made ofmagnesium oxide, the crucible was covered with a lid made of magnesiumoxide, and then, the pellet was subjected to main firing in an electricmuffle furnace FP311 manufactured by Yamato Scientific Co., Ltd. Themain firing conditions were set to 950° C. and 8 hours. Subsequently,the electric muffle furnace was gradually cooled to room temperature,and then, the disk-shaped solid electrolyte having a diameter of about9.5 mm and a thickness of about 600 μm was taken out from the crucible.

The formulation and the crystal phase of each of the solid electrolytesof the respective Examples and the respective Comparative Examples arecollectively shown in Table 1. The crystal phase of the solidelectrolyte was specified from an X-ray diffraction pattern obtained bythe measurement using an X-ray diffractometer X′Pert-PRO manufactured byKoninklijke Philips N.V. In Table 1, a tetragonal crystal structure isdenoted by “t”, and a cubic crystal structure is denoted by “c”. Notethat the content of the oxoacid compound in each of the solidelectrolytes of the respective Examples and the respective ComparativeExamples was 10 ppm or less. Further, the content of the solvent in eachof the calcined bodies according to the respective Examples and therespective Comparative Examples was 0.1 mass % or less. In addition,when a portion of each of the calcined bodies according to therespective Examples was measured by TG-DTA at a temperature raising rateof 10° C./min, only one exothermic peak was observed in a range of 300°C. or higher and 1,000° C. or lower in all the cases. From the results,it can be said that the calcined bodies according to the respectiveExamples are constituted by a substantially single crystal phase.

TABLE 1 Value of x in Value of z in compositional compositional Crystalformula (1) formula (1) Formulation of solid electrolyte phase Example 10.35 0.15 Li_(6.15)La₃(Zr_(1.5)W_(0.35)Ta_(0.15))O₁₂ c Example 2 0.350.15 Li_(6.15)La₃(Zr_(1.5)W_(0.35)Nb_(0.15))O₁₂ c Example 3 0.35 0.15Li_(6.15)La₃(Zr_(1.5)W_(0.35)Sb_(0.15))O₁₂ c Example 4 0.60 0.05Li_(5.75)La₃(Zr_(1.35)W_(0.6)Nb_(0.05))O₁₂ c Example 5 0.10 0.25Li_(6.55)La₃(Zr_(1.65)W_(0.1)Ta_(0.25))O₁₂ c Example 6 0.25 0.10Li_(6.4)La₃(Zr_(1.65)W_(0.25)Sb_(0.1))O₁₂ c Example 7 0.35 0.15Li_(6.15)La₃(Zr_(1.5)W_(0.35)Nb_(0.13)Ta_(0.02))O₁₂ c Example 8 0.100.05 Li_(6.75)La₃(Zr_(1.85)W_(0.10)Nb_(0.05))O₁₂ c Example 9 0.58 0.25Li_(5.59)La₃(Zr_(1.17)W_(0.58)Sb_(0.25))O₁₂ c Comparative 0.45 —Li_(6.1)La₃(Zr_(1.5)W_(0.45))O₁₂ c Example 1 Comparative 0.05 0.15Li_(6.75)La₃(Zr_(1.8)W_(0.05)Ta_(0.15))O₁₂ t Example 2 Comparative 0.350.30 Li₆La₃(Zr_(1.35)W_(0.35)Sb_(0.3))O₁₂ c Example 3 Comparative 0.650.30 Li_(5.4)La₃(Zr_(1.05)W_(0.65)Nb_(0.3))O₁₂ c Example 4 Comparative —0.25 Li_(6.75)La₃(Zr_(1.75)Nb_(0.25))O₁₂ t Example 5

[6-4] Evaluation of Solid Electrolyte [6-4-1] Evaluation of TotalLithium Ion Conductivity

With respect to each of the disk-shaped solid electrolytes of therespective Examples and the respective Comparative Examples, a circularlithium metal foil having a diameter of 5 mm was pressed against bothfaces, whereby activated electrodes were formed.

Then, an electrochemical impedance was measured using an AC impedanceanalyzer Solartron 1260 (manufactured by Solartron Analytical, Inc.),and the total lithium ion conductivity was determined.

The measurement of the electrochemical impedance was performed at an ACamplitude of 10 mV in a frequency range from 107 Hz to 10⁻¹ Hz. Thetotal lithium ion conductivity obtained by the measurement of theelectrochemical impedance includes the bulk lithium ion conductivity andthe grain boundary lithium ion conductivity in the solid electrolyte.

These results are collectively shown in Table 2.

TABLE 2 Lithium ion conductivity [S · cm⁻¹] Bulk lithium ion Totallithium ion conductivity conductivity Example 1 3.5 × 10⁻³ 1.9 × 10⁻³Example 2 2.4 × 10⁻³ 1.7 × 10⁻³ Example 3 2.2 × 10⁻³ 1.4 × 10⁻³ Example4 2.0 × 10⁻³ 1.3 × 10⁻³ Example 5 1.7 × 10⁻³ 1.2 × 10⁻³ Example 6 1.9 ×10⁻³ 1.3 × 10⁻³ Example 7 3.3 × 10⁻³ 1.8 × 10⁻³ Example 8 1.8 × 10⁻³ 1.2× 10⁻³ Example 9 2.1 × 10⁻³ 1.4 × 10⁻³ Comparative Example 1 7.7 × 10⁻⁴6.4 × 10⁻⁴ Comparative Example 2 3.7 × 10⁻⁵ 2.5 × 10⁻⁵ ComparativeExample 3 3.0 × 10⁻⁵ 1.9 × 10⁻⁵ Comparative Example 4 4.0 × 10⁻⁵ 2.8 ×10⁻⁵ Comparative Example 5 — 3.0 × 10⁻⁵

As apparent from Table 2, Examples 1 to 9 in which W and the M werecontained at a predetermined ratio all had an excellent conductivity. Onthe other hand, Comparative Example 1 in which the M was not contained,Comparative Example 2 in which the content of W was too low, ComparativeExamples 3 and 4 in which the content of the M was too high, ComparativeExample 4 in which the content of W was too high, and ComparativeExample 5 in which W was not contained all had a poor lithium ionconductivity.

[6-4-2] Evaluation of Potential Window

With respect to each of the disk-shaped solid electrolytes of therespective Examples, a lithium metal foil was bonded to one face and acopper foil was bonded to the other face, and the resultant was used asan electrochemical measurement cell. The CV measurement was performedusing an electrochemical measurement device AUTOLAB (manufactured byMetrohm Autolab, Inc.). A reference electrode and a counter electrodewere coupled to the lithium metal foil, and also a working electrode wascoupled to the copper foil. The potential (−3.06 V vs. SHE) of thelithium metal was set to 0 V, and a response current was measured whilesweeping the potential at a rate of 0.04 V/sec in a range from −1 to 5V.

The CV measurement was performed, and a sweep potential-response currentin the second cycle in which the lithium ion concentration distributionis equilibrated was plotted as shown in FIG. 20. As a result of themeasurement, two peaks were observed in the redox response current, anda reduction current for reducing and depositing a lithium ion as lithiummetal when the potential sweep direction is 0→−1 V, and an oxidationcurrent accompanying the ionization of lithium metal when the potentialsweep direction is 0→1 V seemed to correspond to the respective peaks.Although a slight deviation from a potential of 0 V is observed in bothcurrents, it is inferred that this is caused by activation energyaccompanying a redox reaction or an overvoltage including an interfaceresistance with an electrode or an ohmic drop.

On the other hand, the response current other than the redox of lithiummetal was less than the detection limit between −1 and 5 V, andtherefore, the solid electrolytes of the respective Examples are eachconsidered to be a stable solid electrolyte which conducts only lithiumions at 0 to 4 V (vs. SHE) that is the working potential range of thebattery.

Incidentally, it is considered that a peak in the vicinity of No. 2 toNo. 3 in the CV curve shown in FIG. 20 represents a reduction depositioncurrent from a lithium ion to lithium metal, and a peak in the vicinityof No. 4 to No. 5 represents an oxidation dissolution current forionizing and dissolving lithium metal. A peak current attributed to aredox response current of a crystal component itself of each of thesolid electrolytes of the respective Examples is not observed. Note thatat a potential at which lithium ion⇔lithium metal occurs, a batteryoperation is not practically performed.

[7] Production of Solid Electrolyte-Coated Positive Electrode ActiveMaterial Powder Example 10

A precursor solution prepared in the same manner as described in theabove Example 1, and LiCoO₂ particles as a positive electrode activematerial for a lithium-ion secondary battery were prepared and mixed ata predetermined ratio, and then, subjected to ultrasonic dispersion for2 hours at 55° C. under the conditions of an oscillation frequency of 38kHz and an output of 80 W using an ultrasonic cleaner with a temperatureadjusting function, US-1 manufactured by AS ONE Corporation.

Thereafter, the resultant was centrifuged at 10,000 rpm for 3 minutesusing a centrifuge, and the supernatant was removed.

The obtained precipitate was transferred to a crucible made of magnesiumoxide, the crucible was covered with a lid, and by using an atmospherecontrolled furnace, while supplying dry air at a flow rate of 1 L/min,the precipitate was fired at 360° C. for 30 minutes, and thereafterfired at 540° C. for 1 hour, and thereafter fired at 900° C. for 3hours, and then, cooled to room temperature. By doing this, a solidelectrolyte-coated positive electrode active material powder containingmany constituent particles in which the LiCoO₂ particles that are baseparticles were each coated with a coating layer constituted by agarnet-type solid electrolyte represented byLi_(6.15)La₃(Zr_(1.5)W_(0.35)Ta_(0.15))O₁₂ was obtained.

Examples 11 and 12

Solid electrolyte-coated positive electrode active material powders wereproduced in the same manner as in the above Example 10 except that thethickness of the coating layer was changed by adjusting the mixing ratioof the precursor solution and the LiCoO₂ particles.

Example 13

A solid electrolyte-coated positive electrode active material powder wasproduced in the same manner as in the above Example 12 except thatLiNi_(0.5)Co_(0.2)Mn_(0.3)O₂ particles were used in place of the LiCoO₂particles as the positive electrode active material for a lithium-ionsecondary battery.

Comparative Example 6

In this Comparative Example, a coating layer was not formed for LiCoO₂particles as the positive electrode active material for a lithium-ionsecondary battery, and an aggregate of the LiCoO₂ particles weredirectly used as a positive electrode active material powder. In otherwords, a positive electrode active material powder that is not coatedwith a solid electrolyte was prepared in place of a solidelectrolyte-coated positive electrode active material powder.

Comparative Example 7

By using a sputtering device, a coating layer constituted by LiNbO₃ thatis a solid electrolyte was deposited to a thickness of 4 nm at surfacesof LiCoO₂ particles as the positive electrode active material for alithium-ion secondary battery, whereby a solid electrolyte-coatedpositive electrode active material powder was prepared.

Comparative Example 8

In this Comparative Example, a coating layer was not formed forLiNi_(0.5)Co_(0.2)Mn_(0.3)O₂ particles as the positive electrode activematerial for a lithium-ion secondary battery, and an aggregate of theLiNi_(0.5)Co_(0.2)Mn_(0.3)O₂ particles were directly used as a positiveelectrode active material powder. In other words, a positive electrodeactive material powder that is not coated with a solid electrolyte wasprepared in place of a solid electrolyte-coated positive electrodeactive material powder.

In all the solid electrolyte-coated positive electrode active materialpowders according to Examples 10 to 13 and Comparative Example 7 and thepositive electrode active material powders according to ComparativeExamples 6 and 8 obtained as described above, the content of the solventwas 0.1 mass % or less, and the content of oxoanions was 100 ppm orless. Further, when reflection electron images were obtained bymeasurement using a field-emission scanning electron microscope with EDS(manufactured by JEOL Ltd.), none was observed at the surface of thepositive electrode active material powder in which a coating layer wasnot formed.

In the constituent particles of the solid electrolyte-coated positiveelectrode active material powder in which the coating layer ofLi_(6.15)La₃(Zr_(1.5)W_(0.35)Ta_(0.15))O₁₂ was formed at the surfaces ofthe LiCoO₂ particles, a white contrast was observed at the surfaces. Asthe concentration increased, the white contrast increased. This isconsidered to be Li_(6.15)La₃(Zr_(1.5)W_(0.35)Ta_(0.15))O₁₂ generatedfrom the precursor. From an X-ray diffractometer, only a diffractionline attributed to LiCoO₂ was confirmed in each particle, and therefore,the film thickness of the coating layer is considered to be thin to suchan extent that the diffraction intensity derived fromLi_(6.15)La₃(Zr_(1.5)W_(0.35)Ta_(0.15))O₁₂ is below the lower detectionlimit. According to the above field-emission scanning electronmicroscope with EDS (manufactured by JEOL Ltd.), the coating layer wasthin, and W and Ta whose content was low were not detected, however, Laand Zr were detected at the surfaces of the LiCoO₂ particles. Based onthe compositional ratio of Li_(6.15)La₃(Zr_(1.5)W_(0.35)Ta_(0.15))O₁₂,the compositional ratio of La to Zr is 3:1.5, and the content ratio ofLa to Zr detected by this measurement was 3.4:1 in molar ratio, andtherefore, the compositional ratio substantially coincides therewith, sothat Li_(6.15)La₃(Zr_(1.5)W_(0.35)Ta_(0.15))O₁₂ is considered to begenerated. Further, when with respect to the coating layers after thefirst heating step in the process for producing the solidelectrolyte-coated positive electrode active material powders of theabove Examples 10 to 13, measurement was performed using TG-DTA at atemperature raising rate of 10° C./min, only one exothermic peak wasobserved in a range of 300° C. or higher and 1,000° C. or lower in allthe cases. From the results, it can be said that in the above Examples10 to 13, the coating layer after the first heating step is formed froma substantially single crystal phase. In the above Examples 10 to 13,the coating layer of the constituent particle of the finally obtainedsolid electrolyte-coated positive electrode active material powder wasconstituted by a solid electrolyte having a garnet-type crystal phase,however, the precursor oxide constituting the coating layer after thefirst heating step had a pyrochlore-type crystal. In the above Examples10 to 13, the content of the liquid component contained in thecomposition after the first heating step was 0.1 mass % or less in allthe cases. In addition, in the above Examples 10 to 13, the crystalgrain diameter of the oxide contained in the coating layer after thefirst heating step was 20 nm or more and 160 nm or less in all thecases.

The configurations of the solid electrolyte-coated positive electrodeactive material powders according to Examples 10 to 13 and ComparativeExample 7 and the positive electrode active material powders accordingto Comparative Examples 6 and 8 are collectively shown in Table 3.

TABLE 3 Base particles Coating layer Average particle ThicknessFormulation diameter D [μm] Formulation Crystal phase T [nm] T/D Example10 LiCoO₂ 7.0 Li_(6.15)La₃(Zr_(1.5)W_(0.35)Ta_(0.15))O₁₂ garnet-type 4.8 0.0007 Example 11 LiCoO₂ 7.0Li_(6.15)La₃(Zr_(1.5)W_(0.35)Ta_(0.15))O₁₂ garnet-type 22.6 0.0032Example 12 LiCoO₂ 7.0 Li_(6.15)La₃(Zr_(1.5)W_(0.35)Ta_(0.15))O₁₂garnet-type 36.2 0.0052 Example 13 LiNi_(0.5)Co_(0.2)Mn_(0.3)O₂ 7.0Li_(6.15)La₃(Zr_(1.5)W_(0.35)Ta_(0.15))O₁₂ garnet-type 30.3 0.0043Comparative LiCoO₂ 7.0 — — — — Example 6 Comparative LiCoO₂ 7.0 LiNbO₃trigonal system  3.0 0.0004 Example 7 ComparativeLiNi_(0.5)Co_(0.2)Mn_(0.3)O₂ 7.0 — — — — Example 8

[8] Evaluation of Solid Electrolyte-Coated Positive Electrode ActiveMaterial Powder

By using each of the solid electrolyte-coated positive electrode activematerial powders according to Examples 10 to 13 and Comparative Example7 obtained as described above, electrical measurement cells wereproduced as follows. Further, in the following description, a case wherethe solid electrolyte-coated positive electrode active material powderswere used will be described, however, also with respect to ComparativeExamples 6 and 8, electrical measurement cells were produced in the samemanner except that the positive electrode active material powder wasused in place of the solid electrolyte-coated positive electrode activematerial powder.

First, the solid electrolyte-coated positive electrode active materialpowder was powder-mixed with acetylene black (DENKA BLACK, manufacturedby Denka Company Limited) that is an electric conduction assistant, andthen, further a n-methylpyrrolidinone solution of 10 mass %polyvinylidene fluoride (manufactured by Sigma-Aldrich Japan) was addedthereto, whereby a slurry was obtained. The content ratio of the solidelectrolyte-coated positive electrode active material powder, acetyleneblack, and polyvinylidene fluoride in the obtained slutty was 90:5:5 inmass ratio.

Subsequently, the slurry was applied onto an aluminum foil and driedunder vacuum, whereby a positive electrode was formed.

The formed positive electrode was punched into a disk shape with adiameter of 13 mm, and Celgard #2400 (manufactured by Asahi KaseiCorporation) as a separator was overlapped therewith. Then, an organicelectrolyte solution containing LiPF₆ as a solute, and also containingethylene carbonate and diethylene carbonate as nonaqueous solvents wasinjected, and as a negative electrode, a lithium metal foil manufacturedby Honjo Metal Co., Ltd. was enclosed in a CR2032 coil cell, whereby anelectrical measurement cell was obtained. As the organic electrolytesolution, LBG-96533 manufactured by Kishida Chemical Co., Ltd. was used.

Thereafter, the obtained electrical measurement cell was coupled to abattery charge-discharge evaluation system HJ1001SD8 manufactured byHokuto Denko Corporation, and as CCCV charge and CC discharge, 0.2C: 8cycles, 0.5C: 5 cycles, 1C: 5 cycles, 2C: 5 cycles, 3C: 5 cycles, 5C: 5cycles, 8C: 5 cycles, 10C: 5 cycles, 16C: 5 cycles, and 0.2C: 5 cycleswere performed. After cycles were repeated at the same C-rate, thecharge-discharge characteristics were evaluated by a method ofincreasing the C-rate. The charge-discharge current at that time was setby calculation using 137 mAh/g as the actual capacity of LiCoO₂ and 160mAh/g as the actual capacity of NCM523 based on the weight of thepositive electrode active material of each cell.

The discharge capacity at 16C discharge in the fifth cycle iscollectively shown in Table 4. It can be said that as this numericalvalue is larger, the charge-discharge performance at a high load isexcellent.

TABLE 4 Discharge capacity at 16 C discharge in 5th cycle [mAh] Example10 111 Example 11 115 Example 12 105 Example 13 43 Comparative Example 662 Comparative Example 7 80 (however, capacity decreased at low loadside) Comparative Example 8 19

As apparent from Table 4, according to the present disclosure, excellentresults were obtained. On the other hand, in Comparative Examples,satisfactory results could not be obtained. More specifically, incomparison of Examples 10 to 12 with Comparative Examples 6 and 7, inwhich the LiCoO₂ particles were used as the positive electrode activematerial for a lithium-ion secondary battery, an apparently excellentresult was obtained in Examples 10 to 12 as compared with ComparativeExamples 6 and 7. In comparison of Example 13 with Comparative Example8, in which the LiNi_(0.5)Co_(0.2)Mn_(0.3)O₂ particles were used as thepositive electrode active material for a lithium-ion secondary battery,an apparently excellent result was obtained in Example 13 as comparedwith Comparative Example 8.

Further, solid electrolyte-coated positive electrode active materialpowders were produced in the same manner as in the above Examples 10 to13 except that each of the precursor solutions prepared in the samemanner as described in the above Examples 2 to 9 was used in place ofthe precursor solution prepared in the same manner as described in theabove Example 1, and evaluation was performed in the same manner as inthe above [8] with respect to the solid electrolyte-coated positiveelectrode active material powders, similar results as those of the aboveExamples 10 to 13 were obtained.

What is claimed is:
 1. A solid electrolyte, represented by the followingcompositional formula (1):Li_(7-2x-z)La₃(Zr_(2-x-z)W_(x)M_(z))O₁₂  (1) wherein x and z satisfy0.10≤x≤0.60 and 0.00<z≤0.25, and M is at least one type of elementselected from the group consisting of Nb, Ta, and Sb.
 2. A method forproducing a solid electrolyte comprising: a mixing step of mixingmultiple types of raw materials containing metal elements included inthe following compositional formula (1), thereby obtaining a mixture; afirst heating step of subjecting the mixture to a first heatingtreatment thereby forming a calcined body; and a second heating step ofsubjecting the calcined body to a second heating treatment therebyforming a crystalline solid electrolyte represented by the followingcompositional formula (1):Li_(7-2x-z)La₃(Zr_(2-x-z)W_(x)M_(z))O₁₂  (1) wherein x and z satisfy0.10≤x≤0.60 and 0.00<z≤0.25, and M is at least one type of elementselected from the group consisting of Nb, Ta, and Sb.
 3. The method forproducing a solid electrolyte according to claim 2, wherein a heatingtemperature in the first heating step is 500° C. or higher and 650° C.or lower.
 4. The method for producing a solid electrolyte according toclaim 2, wherein a heating temperature in the second heating step is800° C. or higher and 1000° C. or lower.
 5. A composite body,comprising: an active material; and the solid electrolyte according toclaim 1 that coats a part of a surface of the active material.